It helps to write for them as if they were seperate from the orchestra. That is, they should sound good on their own. So look at the harmonies as static vertical chords. If there are notes in lower registers, are they widely spaced as they should be? And do they support the other winds playing higher notes in more tightly spaced intervals, like thirds. Even if a particular "chord" is not really a chord, maybe just some passing tones, using what I said as a guideline will give you better results in general. Why? Because the harmonics of the lower notes may acually be fundamentals of the higher notes, making a strong foundation.
And also, like singers, winds have different sounding registers. The clarion and high registers of the clarinet can cut through pretty well, but not so much the Chalameau and Throat registers. Two reading recommendations: Stravinsky's Octet and Symphony for Piano and Wind Instruments. Good Luckwith your winds