Play slower than normal and be fast when it counts. Make good use of your full jump if you want to do aerials. Nair is ... pretty useless unless it's in a combo, same with the knee, and your D-air is limited when Sheik is paying attention to spacing. B-air is a solid priority and speed move, and learning to combo out of it is semi-money. Also, never attempt to just jump at Sheik and do ****, you'll get owned.
Other than that, Sheik ***** Falcon, so don't mess around. You have to be PATIENT, get alot of grabs, and kill at low percents. Ya'll should know how to edgeguard Sheik - just edgehog and knee or forward smash all day.