There are various kinds of IF in the world. Some ask you to solve puzzles; some move you through a specific plot; some encourage you to explore.
In games with a lot of challenging puzzles, you can expect to spend a fair amount of time wandering around trying to figure out what you should do next; this is part of the fun.
Always read documentation.
If the game comes with a read-me file, do read it before playing. Less obviously, some games mention in the opening text that you should type ABOUT, INFO, or HELP when you play for the first time. This information may include special commands or other material without which you won't be able to finish. It is like the game manual in a commercial game, so don't ignore it.
Pay attention to the introductory text.
Most games open with a paragraph (or several paragraphs) establishing the background of the game and telling you a little about the setting and your motivations. Be ready to take a hint from this text. If it tells you that you're looking for money, perhaps your goal during the game will be to collect valuable items. If it says you're trying to recover your lost map of Paris, then that should be your agenda at the start of the game. Other goals may come into play later, but this is where you should start.
Look around you.
Usually the first thing the game will do, after printing the introductory text, is print a description of the room you're starting in. This description will almost certainly contain two vital kinds of information: what the room's exits are, and what things are in the room that you can interact with. (See the first room of the transcript for an example of this.) Authors have various conventional ways of drawing special attention to the things they consider most important. For instance, things that are described more fully, or appear on their own separate line of text, or at the end of a description, are likely to be more significant than the other things described as present in the room.
Check out the important items.
Now that you've identified some interesting things in the room, try examining them. Getting a description of each thing will give you more information. Again, the more detailed the description, the more likely that the item has some significance in the game.
Within the first few moves of the game, you should also check to see what your character is holding initially, using the INVENTORY command. If there is anything, you should examine each of those items in turn. These items can fill a number of purposes: telling you what your goal in the game is, sketching out some details of your character, or providing you with tools, for instance.
Your player character may have an interesting description.
Take anything you can.
Especially in the more puzzle-oriented games, you should cultivate the disposition of a magpie and take everything the game will let you take. Things that can be taken are often listed at the end of the room description, though you should try grabbing anything that isn't nailed down. If it looks useful in some way, it almost certainly will be.
Go into all the rooms that are accessible, and repeat the process of examining and fiddling with things.
See anything you want to do, but can't manage quite yet? This could be a tempting cheese placed too high to reach, or a locked door for which you haven't got a key yet, or a bridge that tantalizingly goes partway out over an abyss and then breaks off. It could be a room guarded by a surly dog, or a treasure chest tied shut with an intricate knot. All these things present you with a puzzle, something you know you want to accomplish, but can't see how to do.
Try any obvious actions.
Are there buttons to press, or levers to pull? Cabinets to try opening? Trees to climb? If it seems like there's something interesting you can do with the items you have before you, you should try them.
Pay attention to the feedback you get.
If you always get the same boring response when you try something, then you're probably approaching it the wrong way. Maybe there's nothing to be gained by that action after all. But if you're told that something happens, even if it's not quite what you wanted to have happen - the dog wags his tail at you, but refuses to get out of your way - then you're probably on the right track. You should try some variations on this action.
Watch for explicit hints.
If you do something and it doesn't work, but the game tells you why it doesn't work, you may be able to use this information to do better next time. Say you get, "You show the dog the apple, but it doesn't seem interested. Maybe something else would hold its attention better." This is a hint from the game that you should look for something else to give the dog that would interest it more. Maybe there's a steak in the next room.
If you get stuck, work on a different puzzle.
Some puzzles you will be able to solve right away; some you might have to wait to solve until you have accomplished something else first. Perhaps you cannot get past the surly dog until you have unlocked the refrigerator containing the steak, for instance. If you find yourself stuck on every puzzle you can find at the moment, try the techniques below, under "What to Do If You Get Stuck".
SAVE when you've made important progress.
Whenever you've done something that advanced your position, you should consider saving a copy of the game. That way if you make a mistake, you can RESTORE and come back to this point. Many players keep a number of saved positions around, just to keep their options open. There's no limit to how many saves you can have.
There's no penalty for experimentation. If you think that something is going to be dangerous, you can save the game first and restore later if things go wrong. Many recent games also support UNDO, allowing you to take back any moves whose outcome you didn't like.
Examine every object mentioned in room descriptions, and everything in your inventory. Look inside all closed containers. Open all doors and go through them. If anything is locked, that's probably a puzzle, and you should try to get it unlocked.
If you still can't figure out what to do, try opening windows, looking under beds, behind curtains etc. Sometimes objects are well-hidden.
Look back at things you've already seen; sometimes this will trigger an idea you hadn't thought of.
Take hints from the prose of the game.
Things that are described in great detail are probably more important than things that are given one-liners. Play with those objects. If a machine is described as having component parts, look at the parts, and try manipulating them. Likewise, notice the verbs that the game itself uses. Try using those yourself. Games often include special verbs-the names of magic spells, or other special commands. There's no harm in attempting something if the game mentions it.
If you have something in mind that you want to do, but can't get the game to respond, try alternative wordings. Often synonyms are provided. Game designers usually try to anticipate all the synonyms you are likely to come up with, but they may not have thought of yours.
Sometimes an action doesn't work, but does produce some kind of unusual result. These are often indications that you're on the right track, even if you haven't figured out quite the right approach yet. Pressing the red button alone may only cause a grinding noise from inside the wall, so perhaps pressing the blue and then the red will open the secret door.
Try to understand the game's internal logic.
Sometimes there is a system in play that does not operate in the normal world-a kind of magic, for instance, or technology we don't have on modern-day earth. If you've been introduced to such a system in the game, ask yourself how you might apply it to the situations that are still causing you problems.
Check the whole screen.
Are there extra windows besides the main window? What's going on in those? Check out the status bar, if there is one-it may contain the name of the room you're in, your score, the time of day, your character's state of health, or some other important information. If there's something up there, it's worth paying attention to that, too. When and where does it change? Why is it significant? If the bar is describing your character's health, you can bet there is probably a point at which that will be important.
Consider the genre of the game.
Mysteries, romances, and thrillers all have their own types of action and motivation. What are you trying to do, and how do conventional characters go about doing that? What's the right sort of behavior for a detective/romance heroine/spy?
Take a break and come back later.
Many players report banging their head against a puzzle for hours, only to realize what the solution was only after they'd walked away from the game. Sometimes your mind just needs to work on the problem for a while in the background.
Play with someone else.
Two heads are usually better than one.
Try typing HINT, HELP, INFO, ABOUT.
One or more of these are often implemented as a source of suggestions about how to get past difficult spots. If that doesn't work, try emailing the author or (better yet) posting a request for hints on the newsgroup rec.games.int-fiction. For best results, put the name of the game you want help with in the subject line; then leave a page or so of blank "spoiler space" (so that no one will read about where you got to in the game unless they've already played it), and describe your problem as clearly as possible. Someone will probably be able to tell you how to get around it.
If you're stuck somewhere that just makes no sense at all, it's possible that you're facing a bug. If you think you are, you should email the author (politely) to report the problem and ask for a way around it.
If difficult or puzzling games are not your thing, try asking on rec.games.int-fiction for recommendations of works that are more narrative-oriented or geared towards exploration. You may in particular wish to try Photopia, Galatea, Rameses, Masquerade, The Kissing Bandit, My Angel, or All Roads.
Much of modern amateur IF is written using an IF design system such as TADS, Inform, or Hugo. Once a game is written, it is compiled into a "game file". The game file can be used on any computer system for which there is an "interpreter": the interpreter is a program that takes the game file and allows you to play it on your particular computer.
If you plan to play a lot of IF, you will want to download an interpreter (once) and then a bunch of game files. All the game files produced by the same system will run (pretty much) on the same interpreter. So if you have a TADS interpreter for your machine, you will be able to play any of the hundreds of TADS games, and will only have to download a new game file, not a new executable, each time. (This makes downloads substantially smaller.)
To walk yourself through the details of getting interpreters, go to Fredrik Ramsberg's guide.