The rule of thumb has always been to apply a good coat of primer, sand, then apply your color coats. This is still a good rule to follow, but new paint technologies have combined primer and paint into one product, which manufacturers assert will cut down on the number of coats you will have to apply. This newer paint is more expensive, but may be comparable to the purchase of separate primer and paint. Look at reviews of these newer paints, particular from folks that have used it in your area.
Climate is another factor to consider. Sunlight, wind, rain and salty weather can all wear out exterior paint. Oil-based paint is durable against wind, rain and temperature changes, but sunlight tends to degrade it. Alkyd paint chalks and sheds very thin layers when it begins to wear. Latex paint is the more durable option for very sun-drenched and relatively dry climate areas. Latex paint with high vinyl content should be avoided, however. Acrylic resin is by far the more durable binder for outdoor latex paint. House Painting Arvada CO
The other difficult part is getting a painting contractor to show up. While this generalization does not apply to every painter, you can rarely get a paint contractor to show up to look at the house and to later produce a written estimate. It's hardly the fault of the painting contractors; it is a combination of the contractors being smaller operations along with a high demand for their work. House Painting Arvada