This. Do not take solely percentage-based pay unless it's a pet project, it's guaranteed to be a major success (I'm talking like MineCraft level success) or the developer is a friend of yours and you're willing to do it for some pizza up front. Percent-based perks can be cool though ("in addition to $X, you get X% of sales/kickstarter fund/etc."). Also, nothing is ever free. If people absolutely can't pay you upfront but you really like the project, at least negotiate a trade of some sort. If they're good with video editing, get a music video out of it.

There are exceptions but knowing how to firmly stand on an upfront pay schedule is important. Do stuff for too cheap and you'll undercut, and more importantly DEVALUE, your like-minded fellow musicians/the industry. Everyone has to put their time in, but know when to just say no.

Get paid after rip offing

GET PAID

RIP OFF AS MUCH AS YOU CAN

In my limited experience, I'd say it's more like "write something TO fit" than "write something, hope it fits."  This involves motifs, as people have mentioned, but also involves identifying particular tempos, rhythms, instruments, etc. that evoke the appropriate feelings. Often it can be helpful to look at things other people have done to achieve a similar effect, then imitate or differ to taste. A little bit of homage here and there can also be fun.

As far as developer input, it's nice to get track-by-track descriptions of what they want, but short of that it's good to at least have some guidance as to what music THEY think is effective - sample songs, etc. This is super-obvious, but when you're working for a client, it's important to keep their taste in mind as well as your own - I mean, they did hire you, but it is ultimately their project.

But soundtracking is very much something I'm learning, as well, so I'm looking forward to what people will say in this thread.

for games on devices with small speakers I'd recommend using a kick drum with a nice click on the attack so that it is present in the mix, and also give your bass instrument some high/mid-range frequencies so you can hear that too. LSDJ music, At high bitrates at least, sounds quite good on my little android :3

As far as composing is concerned, I like it when a game ost is connected through common themes appearing in various songs.

This is very important:

Be mindful of the device that the game will be played on. Be mindful of the speakers on that device and their capabilities. Be mindful of the file format and size restrictions, if any. I was producing iPhone games a couple years ago and in order to ensure that the whole game download would be under 20 MB, we had to ensure that any audio files packed with the client would be as small as possible, and in order to do so, I would resample them as mono 22.5Khz - a lot is lost in that process. Also, the iPhone's speaker does not reproduce bass well at all. If a person is using headphones it's fine but with the speaker it's completely lost. So any song that relied on kick drums or melodic basslines was a bad idea. Mid range stuff with light percussion was always the best way to go.

Obvious if you are writing for PC games then none of this is an issue But if it's something to be played in the browser, filesize is definitely a concern and you may as well go with mono anyway.

Hope that helps.

Leitmotifs all the way

http://en.wikipedia.org/wiki/Leitmotif

Play the level/look at screenshot/read description and see what type of music pops into your head. Write songs. Hope they fit.

Accept only as much input as you can manage without making bad music or getting fired.

- signed, a guy who has no professional game music composing experience.

It doesn't just have to be as simple as making songs that fit. For example with the right programming, music in a game can be dynamic, like overlay loops or different music layers when something changes. A basic example of this is in New Super Mario Bros, once you jump on Yoshi, a different drumbeat starts to play over the top of the existing music. Some games will simply switch to a different track when something happens - playing more dramatic music when you are fighting an enemy for example. There are lots of possibilities. Really depends how much effort is there on the programming side.

It's something that's been on my mind lately! I've been composing stuff for free game side-projects for various people at the college I graduated from, but both times I was pretty much handed the reins as far as how I wanted to go about approaching a soundtrack. My question is whether there are better ways to approach soundtracks than "write songs, hope they fit." And how much developer input do you receive/accept if any? I assume it would be a BUNCH, and I'm wondering how you'd go about incorporating the feedback.

I know that generally you'll lay out the areas of the game that need music, and then write songs for each area (menus, play modes, etc.), but I'm just interested in other ways to structure writing a soundtrack! I'M CURIOUS GUYS