There is hundreds, if not thousands of little things that comes into making even a simple-looking game. Movement, collisions, basic A.I. (or something that at least looks like it), alarms, sprite animations, event orders and what they do, learning to create/change variables at the right time and properly accessing them in the most efficient way (this is a big one), making menus, making the game fun, not getting discouraged (that's the most difficult, and there's no tutorial on this one that I know of)...Eventually you will move on to intermediate stuff like shaders, data structures, enums, state machines, loops, and all that stuff... After that, and even before, you'll be able to debug yourself of pretty much anything on your own.
Basically, just learn the right way. Study the problems you come across until you master that pretty good. Be familiar with the principles and think about the potential uses in a broader way. Then continue with your project until you hit the next roadbump (which you will), and repeat the process all over again.
If anything in the list of things I gave makes you go "huh?", then you know what to do: make a fresh project, open the manual, google and a fresh GM session and experiment. Always run stuff in the DEBUGGER, and learn how to use it, it will speed up your learning curve 10x.