well, this advice is all good!
my advice is make little tests, look at games you like (2d games), little programs you like ect. and think about how they did something, then try to replicate it on your own, this is what i do! if u see something you like on the forums and its open source, dont look at the source, first try to make it yourself, and if you get stuck then look at the source. this will help you look at problems in a different way than you normally would. there are no tell all good tuts, its just practice, and develloping your own techniques.
dont try to optimise things too much at first. what i do is make a "rough draft" then look at what can be optimised and make a new draft with more optimisation.
learn what SIN and COS can do (if you dont know), it will help you enormously! learn how to make beziers also, they are pretty useful, even in their simplest form! ive only been using construct since (Aug 02, 2008 2:26 am lol) and i can already say my computer is clogged with cap files i made all over the place.
also, im just curious to know? how old r u? i think i may be the youngest at 14 but i was always curious how old some other members are?
dont worry about not being able to do things at first, you will always get the hang of them sooner of later!