In ASL to talk about a body part you generally just point to it or spell it.
To sign "ARM" you can either just spell it, or you can use the dominant flat hand ("b hand") to show the length of the non-dominant arm. The tips of your fingers brush along the upper-inside edge of your non-dominant arm from the lower bicep to the wrist.
ARM:
HANDS:This sign looks sort of as if you are cutting off your hands at the wrists. Use the pinkie-edge of the right b hand to "slice off" the left hand. Then use the left b-hand to slice off the right hand. (I know that sounds gross, but at least you will remember the sign eh?)
HEAD:
Touch the upper part of your head then touch down near your chin.Note the bend at my large knuckles.
To express the concept of "leg" I recommend you just spell L-E-G.
Another way to indicate "leg" is to simply point to your leg.
Another way is to use your left and right "b hands (closed flat hands)" to show the leg.
LEG:
Notes: