Nice Artworks ..
specially the first ( the linearts part ) .. the ninja guys and the witch
u got pretty good idea to show on paper .. but u need to practise ur hands more ..
my advise .. watch out for the pencil lines
cleaning the line art before coloring will help ya alot
try the levels and the brightness\contrast options
^_^
other than this .. ur doing great ..
keep up the good work ..
and post some works soon
, Best