If you really want to improve your painting, improve your drawing! Often drawing is the foundation of your painting ~ it's a bit like a skeleton holding everything together. If you find drawing a challenge, take a look at this video and give 'gridding up' a try.
Gridding up is a method of recreating an image and has been used by artists for centuries. It can either be used when drawing from a photo or even when drawing from real life (you just need to employ a frame to hold your grid steady!). The idea of the grid is to simplify your image into small sections, which are then more manageable. This makes it easier to keep your image in proportion as often we can make areas to big which stretches the image or too small, which squashes it!
To grid up, all you need is a piece of transparent film - you could use OHP film, acetate sheet or laminate an empty plastic sleeve. Once you have your film you can draw your grid - WARNING!! your grid needs to be accurately drawn otherwise your drawing won't match up properly. Use a sharpie or other permanent marker and most importantly a ruler to draw your grid. If you are a whizz on the computer you could draw yourself a grid using Word, print it out and then get it photocopied onto a plastic film at your local copy shop - which is what I do.
Once you have your grid you need to also grid up your drawing paper - be careful not to make the grid too heavy as you will want to erase it after you have finished drawing. If you make the squares on your grid the same size as the squares on the plastic film, your drawing will appear the same size. If you draw your squares larger on your paper, then you will create an enlargement of your image and if you make them smaller you will create an image which is reduced in size.
Why not have a go and see what you can achieve!