I quite like the dirty blue effect on the bike, at first I thought it was just very messy

But I think it looks kinda cool.
OK tips:
First - try and lessen the obviousness (?) Of that huge decal on the nosecone!!
If you blend in the edges to begin with, and then use some varnishes to lessen the obvious difference in sheen

(There is an article about it I believe)
Next - while the gems look done right, they aren\'t gradated all that well, and especially the white highlights need to more rounded, as you can see where the brush tip has moved as you did them...
Actual painting tips:
AS ALWAYS - thin your paint
Learn to steady your brush when doing details and highlighting - there\'s some good tips (in this section I believe) where Lizcam asked for tips to paint eyes.
The only other tip I can give is practice and patience. Your highlighting and blending skills will develop as you go - it already looks as though you know where to put highlights etc
The colour scheme is nice, without being too busy, and overall, apart from the highlights, it seems quite neat.