Keep this law of my Status System in mind, which has been strongly successful so far for me:
"You level up the fastest and easiest by doing things at your own level and no higher or lower".
In short, start with simple stuff if you're a beginner and do the more complicated stuff when you're more advanced.
Read through the manual and look for instructions that seem to interest you. Then try to use them and modify them. Then find another instruction in the manual you are interested in and look at that. Now try to add that and combine it with the first instruction in some way. Then do a third, a fourth, and so on.
After that, create a new script and try to make something related what you did before in a somewhat different way without referencing your old script as much as you can.
Then keep on adding new instructions to your "instruction vocabulary" and expanding on it.
Now try to create a simple game like pong which has just two blocks that move left and right and a small ball. After some number of hits without the ball going past them, the ball speeds up. If the ball goes past them, a score is made and a new ball appears. That's an example of a simple game.
Go learn some more instructions and try to expand on this game to make more out of it.
Now try for a more complex game, sort of like an NES-type game (which are also rather simple, but more complex). Pick a game you like/know well and try to mimic it the best you can. Now, after you've done that, try to improve your game by adding some new features, some that might not be present in your favorite NES game.
Now try to mimic a more complicated game or create a game on your own with your own rules and game mechanics.
After a while, you could begin making your "official project", the project you intend to sell. Along the way, keep doing things at your own level for learning the fastest and easiest. This law has never failed me yet (hence the "mostly confirmed" status).
If you do something that's too easy (like having tenth-grade skills in first grade), you won't like it and you will barely even learn anything. Think of a tenth-grader in a first-grade classroom doing a spelling test trying to spell the word "walk". To them, it's not even a challenge at all and the tenth-grader would get A's across the report card (102% even) with almost no effort and school would be only boring to them.
If you do something that's too hard (liking being in tenth grade with only first-grade skills), you'll be very frustrated and give up. Think of a first grader trying to solve the quadratic equation. To them, it seems like a random mess that makes no sense. To a first grader, they'll likely only get F's across the report card, they'd be frustrated with school and would just plain give up.
Now, if you're a tenth grader in the tenth grade, then you'll understand all that tenth-grade stuff with some difficulty and some ease. It's like Goldilocks (sp.?) and the three bears. Goldilocks will only find what's right for her. If the porridge is too cold (too easy in a similar sense), she might eat it, but likely won't like it. If the porridge was too hot, she'd likely immediately stop eating it (too hard as you'd give up). If the porridge was just right, she'd eat it and like it.