Good job so far.
Heres some more tips for you to try.
Before you start your next handgunner, have a quick look for 'mold lines' on your mini. Remove them very carefully with a craft knife or file before undercoating. Watch your fingers and make sure you dont miss any areas ( check the inside thighs
Painting is pretty systematic. You need to think like this;
If you bare these 3 phrases in mind you wont go wrong.
Paint your midtone colour first. Go 50/50 water:paint. In your picture, lets look at the trousers. It looks like the midtone colour is Goblin Green. Make sure you get an even, uniform layer of the midtone colour. You do this by building up thin layers of paint, waiting for one layer to dry before doing the next. (dont forget he is wearing shoes btw).
Once you have a flat, uniform midtone, move onto shadows. Look at the mini and decide which areas will be darker than the midtone. So rather than 'wash' the whole are with say badab black, just look for crevasess and creases, inside thighs etc. I would use Thraka green as a shade here, with a drop of badab.
You dont need to water GW washes but you do need to shake them well. Take the wash on your brush, then before you use it, run it across a clean white piece of A4 (taking some wash off). The pooling and tide marks you see sometimes comes from 'flooding' the model.
Once youre happy your shadows are right ( keep adding a little more black each layer and reduce the area you darken each time), tidy up any mistakes with your midtone then go onto the highlight. A good highlight for Goblin Green would be 50:50 goblin and scorpion. So as you did with shadow, think which area would be lighter than the midtone ( where light would hit).
When your happy you picked out your highlights, you can 'glaze' the whole trouser area to bring the highlights, midtone and shadows together. A glaze would be a drop of colour and lots of water added. It should 'tint' the trouser without changing its colour. You could use thraka green, or you might experiment with baal red or assuman blue - remember to use your paper to take excess of your brush.
Anyway sorry to go on, but that is a quick basic painting guide and you'll see a quantum improvement in results if you try it