Well I just wanted to know everyones thoughts like with your Gamemaker mistakes.
What have you learned to do better? Did you still learn?
Well anyway I have learned to take my time on games. I am still working on that. But what have you learned from your mistakes?

Save... often. I've been unfortunate enough to lose up to a week's worth of work because I didn't save regularly. Guess I had to learn the hard way, eh?

Man I have a good one. I save everytime I make a change. Then when the game file is huge I learn my lesson that I have to wait awhile lol.

i learned that you should just do the main game first, than add all the flashy stuff later, before you release it.

another one is that GML takes up less space then D&D.

Believe me I know gml takes up less space. D & D takes up space because of the custrom programming & images.

I learned not to use the draw event for stuff that should be in the step event. (The draw event is executed once for every view and it would cause problems with motion and such) I also learned that you shouldn't save your GM files out in the open. (My brother thought it was trash, so he deleted from my computer.)

Few things:

Indent coding
Don't make redundant coding (e.g. if (a = true) { a = false} if(a = false)
{a = true). That could be a = !a;

Use extensions when naming resources (e.g. not ball, but sprBall)