How to choose colors for exterior painting.

The easiest way to choose a color for your house is to go to a paint store after you get an idea of what you want by looking at color schemes and buy a few samples.
If you are looking for something specific you can drive around your neighborhood and if you like any of the colors you see on your neighbor's house you can always ask the owner a permission to peel of a little piece of paint from inside the trim or at the foundation of the house (that is where a lot of times you can find paint that is already peeling off). And then have a computerized color match done on the peeled off sample in any paint store.

Some people are interested in using ceramic insulating paint. Supposedly it is the paint that reduces the heat from the sun and cools down the house. Besides the claims of the people who sell the paint or profit from the sale in one way or another, there is no evidence to suggest that this type of paint works as advertised. It is not available for sale at any retail store. One can buy this paint only through the internet. For a person doing research on ceramic insulating paint here is a good article. The author of the this article makes a very good argument against the paint with a funny closing in the last paragraph.

Elastomeric paint.

Elastomeric coating can be oil or water based. It it is formulated mostly to cover surface cracks and be a sealant against moisture. For elastomeric coating used in residential painting most often surfaces covered are concrete, brick or stucco. Elastomeric paints usually used in coastal communities where waterproofing is desirable, or areas where it rains a lot during the year. Elastomeric paints usually do not chalk which makes them very long lasting. Being long lasting paints, holding the moisture out and hiding the cracks, those are the advantages of the elastomeric paints.
However there are some disadvantages. 
A gallon of elastomeric paint will cover about 80sf per gallon, when most of the paints used for exterior painting will usually give you 200-300 sf per gallon. In addition of covering very small area per gallon, elastomeric paint is  expensive. It is about $130 for 5 gallons, when premium water based 100% acrylic Dunn Edwards paints start at $85 for 5 gallons (all contractor pricing).
Elastomeric paint requires very good surface preparation and high pressure gas sprayer(most electric sprayers won't do the job).
If moisture gets behind elastomeric paint it may become trapped with nowhere to go, blow up like a balloon and the paint will come off. If moisture gets behind regular paint, it usually cracks and this crack can wait till next painting job, and be fixed during preparation process.
The cost of painting the house with elastomeric paint will be a few times higher, comparing to best premium water based 100% acrylic paints, and in Phoenix metro with so little rain fall will be hard to justify.

Some of the painting mistakes homeowners make, when painting an exterior of a house by themselves.

Exterior painting of a home is almost never a do it yourself project.
The paint exposed to nature elements(sun, heat) and there is just too many reasons why paint could fail if not applied properly, or surface is not properly prepared.
House is not power washed prior to painting or the power washer doesn't have high enough pressure.
Usually power washer with less than 2000 psi(pressure per square inch) will not do a good job in power washing the house. Most gas power washers qualify. Most electric ones have less than 1500psi.
Not scraping loose paint by hand.
If the house has a lot of pealing paint, most of it will come off after the house is power washed. But power washing along will not solve the problem. Scraping loose paint by hand will ensure that all the paint that is about to fall off, will come off before the new paint is applied. Otherwise new paint will fall off with the chunks of an old one.
Not fixing the cracks.
Moisture will get inside the cracks and paint will start pealing.
Not spot priming repaired areas.
The paint will not come off if the surface is not primed. It will look fine and may even hold long enough. But most of the paints manufacured to be the top coat, and with primer underneath it will last much longer.
Not using the right type or of paint or primer. Or the right type but of a low quality products.
There is a variety of different types of paint for a reason. Rod iron prefers oil base paint, wood-100% acrylic paint. Not using the proper type of paint manufactured for a particular surface will reduce the life of a painting job significantly.