I like your spirit, just keep painting if you love it
About this piece: the biggest point of improvement would be to make the left bottom corner much less dark - it's odd that it's so invisible compared to the rest of the piece.
Secondly, try to use less fine/scribbly lines for your objects. You can set them up fatter and straighter (more vector like) and always paint over. The biggest problem with this is that the airplane isn't correct/straight or correct in perspective.
Try to first draw the line art until it is good and correct, before colouring anything.
Hope that makes sense, good luck!