Even if you only play in matches studying unlimited or money doubles is still very important because the equity doesn't shift around as it does in matches. Once you've mastered these you can copy the positions into XG or GNU and try them out at different match scores to see how the cube action changes.
Here I've picked some random double positions and given my own thoughts on how I look at the board and what seems important to me when making a cube action. I categorise the type of position this is, for instance, position 48 is a high anchor where black has made an anchor on the 4 or 5 points. Then my thought process just looking at the board from both sides, then my decision. Where I get it wrong I've written which bit I got wrong. This is vitally important because it is true that you learn from your mistakes and hopefully you'll learn from mine.
I see so many players making cube decisions based on initial gut instinct without taking even a moment to consider the position. The cube is without doubt the most difficult part of the game and takes a lot of effort to really master it. But once you do you will reap the rewards over the board.
I suggest that you play the each of the ten positions in the links below before reading my explanation and see how you do. Then play them again but this time write down how you see the board and what you think are the important factors, then make your cube choice. Afterwards compare your performance with your first try then compare your analysis with mine. It could be that our attention is drawn to similar and also different things. My answers are not wrong or right, they are just my thoughts at the time I looked at the position. And it is true to say that the more times I look at a position the more I see in it.
This isn't meant to be a systematic study method but a fun learning exercise which you can continue on your own using bgquiz or on your own positions.