I've been writing songs quite a lot recently, and basing them on just about anything I can think to draw inspiration from. I've been writing with my musician friend for most of it, and we've actually got a pretty good song going. We pulled our inspiration directly from our environment: School. We toyed with the concept of doing things you don't really want to, or being pressured to go somewhere you don't want to be in life. If you're looking to write a song on something, pull inspiration from absolutely anywhere and see if it sticks. I wrote up a bunch of mock lyrics sitting at my desk after watching "The Warriors" last night, and it seems pretty clever.
Write the chord progression for your song first. No need to stay too basic, but make it appropriate for the song style. For example, sad songs want to be written with emphasis on minor chords, and a blues scale if not pentatonic minor. Pick your key and find a progression that suits your theme and sounds nice to start with, and develop the melody. Once you have a basic pattern for your verses, count the available syllables per sentence/section and then write the lyrics to fit around that. That's how me and my friend have done it, and there was no issue on fitting the lyrics into the time scale. Then, once the chorus and verses are done, work on a solo if you want to have one. (They can be very tough to write for songs, so I'd recommend that you don't bother with fancy solos unless you're talented with scales and all the techniques revolving around them. Instead, replace it with a bridge, where your chord progression can modulate to give a bit of flair but still keep it simple.)
Good luck.