A lot of the essentials and good tips already mentioned, I think the way I would (kind off am) going about this would be in this order:
1. Find your putting form and style. With form, I'd say if you expect to be one of the best, you have to make sure you do the essentials, all the successful pros do wildly different, but they still do the essentials that allow them to get a strong weight shift and a putt with power and also with great consistency. If you already have the form fundamentals that allow you to put from 9 - 12 meters without a lot of effort and strong-arming I would assume you got the fundamentals in. Then the next thing would be to consider consistency and choose the style of putt that gives you the most consistency in all types of weather and mental conditions. Some styles are only great with no wind, some styles are very finesse and hard to do with lots of pressure for some people.
2. If you have the fundamentals down and you stick to one type of style this of itself should lead to improvements by just practicing, if you are not getting improvements, try practice in a different way and I like the advice here about resetting between every putt and putt like one would do in a tournament, this will also help with my 3rd point which is.
3. Build your routine, the routine can have a huge impact on your putt, I like to do a practice swing and feel my weight shift and get my aiming point down and go for it, other people like to just go for it, others might be just staring down the basket forcefully, etc... I think the routine part is about doing whatever makes you feel confident, one of previous parts of my routine has simply just been actually getting my body and posture in a confident posture with my chin up and this really helped my not missing low but also kind of made me feel a little more confident, the mind follow the body and vice versa. One thing to experiment with here can be to consider your weak point, what are your misses? Are you missing right? can you do something in your routine that can help that? are you missing low like in my example? are you nervous and your misses are because of that? well, what can you do in your routine to help with that? maybe not using too much time and just being more casual with your routine can be something to try out... Do you even have a strong routine and what is it?
4. After working on the form (which I think you probably already have locked in) I would work on the way you practice and also practice your routine or contemplate if you should even try changing your routine and then solidify it. I think after all of that the next thing to consider is your mentality, if you're finding that to be an issue, but I definitely would work on routine first because that can often help and eliminate a lot of mental issues and nerves. Even if you don't struggle with this going through how you think about your putts, how your aiming, visualizing and all of that can also be avenues to get even stronger as a putter.
Also, do you love to putt? I think you also need to keep the fun in the practice and learn to love doing it if you want to become the best of the best. I think to get that mentality of looking forward to hitting the putt, instead of being afraid of missing the putt is a huge mental issue with most people.