A good rule of thumb to remember is that putting a mic too close to the sound hole is going to be a bit boomy, not that you can't or shouldn't use that if need be. The thing about uke is it's so small that little movements make huge differences. Experiment with the mic fixed in your favorite "sweet spot" then move the uke around and see what different tones are available, and use them wherever appropriate. You'll find yourself moving in and out depending on if you're strumming hard or fingerpicking, closer for soloing, whatever. It's what I miss now that I'm plugged in. I use a volume pedal for solos now!