Go out and grab yourself a couple of conkers and look at them, draw them, enjoy them. Once you've done that try my image. Watercolour is the medium but it can easily be painted in acrylic. If using acrylic use lighter colours to lighten up tones eg yellow added to brown rather than white, white and black tend to flatten your colours. Enjoy and have game after.
I have used really poor quality watercolour paper bought from Tiger in Carmarthen, I just wanted to show you how important using good paper is. If you are a beginner or just experimenting any paper will do but for this I would recommend some good quality watercolur paper or even some smooth if you can get it.