Here are some tips that will save you time and make a great looking project.

1. Always use a good quality exterior grade plywood. I prefer 1/4" birch flooring underlayment grade plywood for smaller projects that comes in 4' x 5' sheets and 1/2" exterior grade plywood smooth sided that comes in 4' x 8' sheets for larger projects. You can find 1/4" birch plywood at a flooring material supply company or flooring covering retail store. Check your local phone book. Some lumber yard stores will also carry this as well as the 1/2" plywood. Each pattern has it's own material list so you will know what you need to complete any project.
2. You can prime the plywood on both sides with a good exterior paint primer before or after you cut out the pattern. If you prime first, then you can transfer all  the detail & paint lines for the project. If you prime after, then transfer just the "larger cut lines", prime and then transfer all the detail & paint lines.
3. Transfer the pattern to the plywood and cut out. Most of the time a jig saw with a smooth cut blade works best. Depending on the skill level of the pattern, some cuts are very tight and will require the use of a "scroll saw blade" that fits a jig saw and makes it easier to cut out difficult areas.
4. From here it is like a paint by number kit. I use acrylic (water based) paint you can buy at the hardware or lumber store. They usually have a good selection of basic colors in small cans and you can easily mix small amounts for a special color. You will need a set of assorted size paint brushes as well.
5. After you paint all the areas and edges as needed, outline between the colors with a paint marker. These are available in assorted colors and in fine / medium point and work like a magic marker only with paint.
6. To highlight or frost areas, use a technique called "dry brushing", by dipping the brush in paint, then wipe it off on a paper towel so there is hardly any left on it, then lightly brush on as you like.
7. After your all done, give your project a good coat or two of clear finish, satin works best, not glossy.
8. To display outdoors, I screw 2 pieces of 1" x 2"  wood to the back top and bottom area or where ever the project allows. Then I use 1/2" electrical conduit cut to about 2 - 3 feet long that I can pound into the ground (even frozen ground) and attach the project using conduit clamps and screws to the mounting boards on the back.
9. To light up your display, I use colored or clear flood lights that set inside a shadow box so you cannot see where the light comes from and concentrates the light on your project. Also it helps protect the flood lights from the weather.