Here in Thailand weightlifting are not recommended until you stop growing or about 18 years of age.
Regular weightlifting like arms and legs are fine, but I've heard that lifting weight above your shoulder will slow down your growth.
As other said, practice makes perfect.
I'm a pretty consistent player for my age and the only reason behind that is because I've got an indoor basketball court just infront of my neighborhood.
I improved a lot just in 3 years time because I play basketball almost everyday.
So if you play more often, by often I'm talking about 2-3 times per week or more, I guaranteed that you will become twice better than you are now in a year time or even less.
And for left hand layup, before I wasn't able to do them either. However, practice makes perfect

What I do is concentrate on the steps and remain relax. If you put pressure on yourself you wont succeed. Try practicing by start dribbling from the three point line and head towards the basket at 45 degrees. This makes it a lot easier to bank off the glass.
Never be a coward with a better men. If you are scared or unconfident, you will not develop. You have to be confident and got faith in yourself. If you think that you cannot do it, then you will not be able to do it. This is important.
If you dont know when to pass, what I strongly suggest from my own experience is, dont hold onto the ball for too long. When opening a play try to pass it to your nearby teammates first. Dont try to pass it to someone under the basket and get an assists. The important thing is, dont always aim to get an assists. It's not that important. What's more important is how you make your teammates better by helping create space for them with good passes. Remember, assists is not your main goal. As I said, dont make a bullet pass to the player under the basket straight away. Set up the ball movement continously by passing it in one direction first. If the ball came to a dead end it will most likely return to you. And when this happens, you can start the ball flow again. Another thing is, do not hesitate. If you want to pass then do it quick. If you hesitate for even half a second the defense will be able to read your mind since they see it coming. When making a pass, you dont only see the player you're passing to but you must also see the defense and whether or not they can intercept your pass.
When you dont have the ball, you should be making cut to free yourself up. However, if your teammates is struggling with the ball, you have to help him out by running to him in a way that he can feed you the ball. Always keep an open eyes out incase someone need you. A good PG always try to help their teammates when they are in trouble. If they are struggling with the ball, your job is to get the ball and set it up again.
To be a good clutch player, you have to understand the situation you're in first. You'll learn more and more from experiences. The important thing is to trust yourself. Impossible is nothing.
Dont think about you being short. Earl Boykins and Nate Robinson are capable of many fantastic things. It's not the height that matters. It's the heart and skills.
What you should develop as well is perimeter shooting. You will find yourself open quite often in the perimeter area. This will help boosts your game and make you much more effective as you can be dangerous on the outside as well.
I hope that helps more or less
