I agree with Jerrman. My procedure for these types of plastic kits is:
1. if possible wash the plastic in warm water and liquid dish detergent.
2. after it has dried and if there are no clear plastic windows or if you can remove them spray with dullcote. This adds 'tooth' for the primer.
3. prime as jerrman says.
4. wherever possible spray or air brush whatever you can. This lays down an even pattern and leaves no brush strokes. If you don't want to spray but have large areas you need to paint try using a synthetic sponge to spread the paint around.
5. if you have to use a brush let the base coats cure for at least 3-5 days. Once again if you can spray dullcote. The dullcote will take the shiny out of the existing paint and once again add 'tooth'. Try to brush in one direction and don't go back over what you have brushed. Let the paint dry then go back over it again.
Joe