Some idea have which might help you in your improvement:
-trying to spend more time on some drawing, for taking more time to observing the subject,
-trying to put more loose in your lines, just take it more easy, sometimes your lines are really heavy, if I make sense,
-trying different technique, for example charcoal, I figured you might enjoy it
Thanks for the advice PaperDragon. Stuff like the ketchup and mustard bottles is meant to be a really quick value study but I've noticed that time spent is practically directly proportional to quality.
I would like to spend time with different techniques. If I get access to an airbrush in the future, which I might, then I'll play around lots with it.