The step from representational to more abstract work is one that artists often find difficult, but once you get to grips with it you will be on the way to creating abstract works in other ways. The first step is to start using a sketchbook to draw and paint your subject either by creating the sketches on site or by using a photo. This allows you to be more free and loose in the way that you express your work and to work more expressively.
If at all possible mix your colours into a small range of tonal mixes before you start painting. This will enable you to paint more quickly and to be more expressive. When you sketch with paint try using the brush in different ways to make different marks, such as using the side of the brush or the front edge or just the point. Each mark thatyou make will be very different. Try to use one mark rather than making numerous marks to convey a shape or tone.