With stuff like this it's usually just a matter of creating a basic loop that i like, either through random experimentation or by going for walks and thinking about a given rhythm or melody for a while until i feel like i have enough of a handle on it to sequence it. After that it's basically like jamming with myself in slow motion, adding melodic and rhythmic parts at random and then taking them out again if i don't like them. Much of the music i've done is basically just the same basic chord progression looped for a while and gradually built upon, with shifts in the basic progression whenever i feel i've fully explored an idea. Really my music is almost embarrassingly simple, structurally. My creative process consists mostly of controlled serendipity so it's hard to give much helpful advice. The most important thing, really, is to experiment, and to persist, even when you suspect that what you're working on is total garbage. It's also helpful to listen to the music of people you admire and pay attention to how they structure things and how they develop their musical ideas. In fact, i think you'll learn more from that than from any of my questionable advice.
Thanks, it's interesting and useful getting an idea on how you do it. I find I often change the basic rythm and chord sequence around too much and it ends up sounding like a horrible mess.
I'll continue listening to other people's work and messing around, see if I can get better at and more comfortable with my aproach.