Hang in there! The principles are the same but the medium is very different. Start by thinning the paint out by adding just a tiny amount of turpentine. Just enough to make the paint slightly more fluid. As you put down successive layers use less turpentine. Put down no more than a couple of brush strokes before loading your brush with fresh clean paint again. If you look at KCHEN(post #41) and fredflickstones(post#17) paintings on the first page of the life painting thread you will see great example of the process. Use a large brush and try to place 1 large stroke that represents an entire plane instead of a several smaller strokes. As you progress through the painting if you want to refine it you can add smaller strokes that transition between 2 larger tones. If you do this rather than blending with brush it will maintain the form better and keep that crisp look(minus the smudges). Maybe if you post some of your stuff I could be more help.
"People never improve unless they look to some standard or example higher or better than themselves." (T Edwards)