What is the best way to seal and prime a wall before starting a mural?
If planning to paint directly onto a concrete or brick wall, an artist should first scrub or blast off all dirt, peeling paint, oil or other contaminates. The next step is to apply a water-based masonry primer, which can be bought in any major hardware store. GOLDEN Acrylics can then be applied to this surface.

I'm preparing to paint a mural onto dry-wall, and I'm debating whether to paint a base of latex paint or acrylic gesso. What's the best method for preparing dry-wall for acrylic paint?
Either one is suitable but for the greatest longevity, apply one or two coats of thinned Gesso (2:1 Gesso:Water) as a primer, then one or two coats of full strength Gesso. If you do decide to use latex primers and paints, buy the best ones you can afford, because no matter how good the artist's paints are, they will only last as long as these underlying coats. Once they start to fail, so will the mural.