This is my recommendation. First make sure you putt on the intended line and aim your clubface square to where you aim. This can be done with an elevated string on a flat slope, make sure you can make the ball roll under the string, make a gate with two pegs at the beginning of the string so you make sure the ball starts where you want. Then try it with some break and notice how much you have to aim outside the cup to sink the putts. With break the ball starts under the string but leaves the string ofcourse. Once you are aware of the true aim, learn some about different putting techniques, the technique where the clubface is square to the target all the time and the more common one when your clubface turns in an arc, also read about different putting grips. Try some different techniques and decide for the one that feels best. Now learn some basics about green reading, how downhill and uphill affects the break etc, also check some videos about aimpoint and maybe take a course if you wanna learn more about greenreading. Next thing is to get the right speed, I don't recomment you to try to learn lot of techniques, this is imo mostly feel and training. I'd train lot of long putts like 10 yard putts from different slopes and combine that with the green reading skills you learned. Then make sure the 3 feet putts is in the cups atleast 90 % of the time. Should be few or none 3 putts after that.