Late reply, I don't visit this forum too much. Anyways, there's a number of elements that make music "fusiony" to me. I'd say harmonic language, melodic language and rhythm. I think the key element is the harmonic language. An intricate harmonic language will dictate your melodic language to follow. You just have to have a good sense of melody and the knowledge to "transform" melodies to fit over different chord changes and so on. I try to avoid tricks like shifting motifs around, that tends to sound so puzzled out and analytical to me. Though from time to time the harmonic content will ask for a simple motif to be shifted around and it sounds good, so I approach it like that. When I'm writing a piece I think of harmony first (writing a chord progression). Melody second (I try to use a very simple melody throughout my harmony by the use of extensions in the chords). After that comes the rhythmic interpretation and last I'd "decorate" the melody hidden within the chords to be a real melody that you can lay on top. Hope this helps!