some very sound advise there barry.
THE most important part being to have a "model hack" i have an old mosquito that i use for making sure i have the right consistancy for spraying and lets just say it would be very well camouflaged against a rainbow!!!
i also have other bits (half a fuleslage, a wing...etc) that i use for other random practices.
even though 99.9% of the time i get it right the first time i still ALWAYS give it a go on the "hack" first of all to prevent and dissapointments on a project.
i find some people after applying an effect squint to see if it looks ok, NEVER do this, as obviously your vision will not be 100% so even though it may look perfect when you squint it may not be with your eyes fully open so dont kid yourself!!!
have a look at the pre-shading video on scaleworkshop. this can help alot, or take a look at colins lighting and buck build...
http://www.scale-models.co.uk/showthread.php?t=2759 (Under construction Buccaneer)