Re: Should I prime before I paint?
I get this question a lot!
If you are changing colors from a dark or bright color to a lighter one, it's best practice to prime the walls first to avoid having to apply multiple coats of paint. Just make sure you tint the primer to 50% of your desired color. Where ever you buy your paint - they will know what it means.

Other times you'll need to prime:
-New wood
-new/resurfaced metal surfaces
-rusted surfaces (cleaned first)
- when walls have stains
-when a smoker lives in the house all walls/surfaces should be primed prior to painting.
Another common question we hear (and is commonly mixed up with primer) is "sealing" and it's benifits.
Sealing a surface in not priming a surface. The idea behind sealing a surface is a little confusing since you are not "sealing" per say, but you are applying a product (the sealer) to an exterior surface in order to chemically change the old paint in such a way that you can paint over it. When a paint becomes chalky (rub your hand on the paint to see if it's chalking), it needs a sealer. Paint over a chalky wall and it's like painting over talcom powder - paint will eventually fail by bubbling or cracking. We've peeled large swatches of paint off walls that were not sealed properly. Simply pressure cleaning the area is typically not enough since a sealer will correct the chalk and help with correcting the ph balance. Surfaces that do not chalk do not necessarily need a sealer.
Hope that helps!