A lot of beginners just don't put enough paint on their palette. Maybe they are afraid to "waste" it? If this is your problem, see the post on this forum that deals with saving paint.
http://forum.portraitartist.com/show...save+and+paint
In the bottom layer(s) of a painting, paint should be thick, buttery and really cover the canvas...just like a large and overgenerous glob of mayonaise covering a slice of bread.
One of the clues that you don't have enough paint on your brush is that your brush makes a lot of noisy scrubbing sounds. I had a teacher once who insisted that we all "paint with a quiet brush" (and this means that your brush will be loaded).