That's a very general question... factors to take into account:
-wheel diameter
-ride height
-camber
-tire expectations dry vs wet traction, hydroplaning resistance, wear, etc.
If your vehicle is lowered you may increase the likely hood of tire rub with wider than factory tires and subsequent fender rolling will be required to correct the issue.
Check out tirerack.com for loads of info about the above as well as info about your options as far as tires go.