The best way to decide if a shirt is too sheer is to stretch the material over your hand and if you can see your hand through it then you might want to move on from it or consider putting a tank top underneath it. Also when looking for a shirt make sure that it "glides" over your curves, not clings. Then when you find the perfect top that is soft, the right length, concealing--buy a couple in all the cute colors because you can wear them with everything!
As far as sleeve lengths go: the length of a sleeve really does completely change the look of a shirt. "You want the sleeve to hit at either a thin point of your arm or at a point where your muscle has peaked and is starting to dwindle. If the sleeve stops at a point on your arm where the muscle is extending out, it will make it look much bigger than it actually is." (Lauren Conrad)
