I normally start with the beat, then a bassline, then some riffs, then work backward and forward in time from there...
A friend of mine starts with the beginning, and adds what he thinks the track needs at each stage. Kinda like listening + producing at the same time... It works really well for him - his arrangement is spot-on, as are his sounds - but he's a progressive type, and I feel as a technique it will bend you towards writing progressive tunes.
Not a completely bad thing! Gonna give it a go myself...
Tequila