Watch the Basic Strums online guitar lesson by Marcy Marxer from Ukulele for Guitar Players
The first rule of strumming is stay relaxed. Relax your fingers, wrist and the muscles in your arm. You’ll get great sound with less effort by staying relaxed.
You can see from the video that I hit the strings of the uke pretty hard. Relaxed control gives me a big sound and I never scratch up my uke.