Check your paint. Is it dimpled, soft, deformed? If so you need to buy fresh paint.
If not, check your velocity. To low, increase it. To high, decrease it.
Last, check your paint-to-bore match. Put a paintball into your barrel and then gently blow into it. If the paintball moves through the barrel with little force, your good. If it takes a lot of force, you need smaller sized paint. If the paintballs go right through the barrel, you need bigger sized paint.
What barrel and paint are you using?