Problems with uneven acrylic paint?

While it's still wet, lightly rub a damp paper towel over your uneven paint. OR use a damp sponge brush to apply your paint 

Dip your paint brush into some water and add it to your paint.
Add as much as you need, but be careful that you don't add too much!

To save time during a craft which involves painting, don't clean your brush every time you take a break. A plastic bag can keep your paint from drying out and the brush bristles pliable for an hour or even over night