Hi Howie, Like everyone has said practice is the key to success you are doing the right thing by getting a book to practice on and also things like coke bottles baked bean cans etc are good for practicing going round corners I would'nt use tap water to thin the paints with only distilled either that or brand of thinners that go with what ever acylic's you are using you won't go wrong with Tamiya or Vallejo both are very forgiving if you mix 50/50 with what ever your using as a thinner you should get a decent result another tip is to cut to air if you want to dry the surface a bit quicker just push the trigger down and it should just be air coming out the nozzle.
Hope this helps a little good luck
Nige