Concrit PLZ? *bambi eyes*

I've thrown myself into messing with my watercolour pencils. Unfortunately - well, let's just say things don't always turn out the way I want them to. I don't have a brilliant sense of colour, for one thing, and as soon as I venture to combine several colours, the results aren't quite what I hoped they would be. The trouble is that I'm not sure how to correct the mistakes I have made, which is why I thought I'd consult the wonderful LJ crowd, who always seem to find answers to the strangest questions :-). Please share your wisdom and help me improve!

( Tonks and Lupin on a couch (G) )