I'm making good progress but two deeply ingrained habits are repeatedly surfacing,1) Bending my fingers upwards at the nail joint (or, more accurately, extending at the DIPJ)
2) Waving my left 5th finger madly in the air, at any speed above about 60bpm
Just got beat somewhat by allthumb ...anyway.If I understand you correctly, your first problem is collapsing of the last finger joint. That is indeed something one should avoid. The first step to retraining is developing a heightened awareness for the problem. A habit is something that happens subconsciously, thus, no effort is involved in making it happen. Habits will therefore go largely unnoticed. So, try to pay attention to this issue. There are two ways. One, if you get into a situation where the habit might be invoked, pause for a second and think about how you would like the movements to be carried out and act accordingly. This is, before the habit gets invoked by your subconscious, switch to a conscious mode. Second, if you catch yourself acting on the bad habit, immediately correct it. Stop there and repeat the action using the proper motions. Over time, you'll be able to catch yourself more reliably when you do bad things, and eventually BEFORE you do bad things. At that point, you will also probably have acquired the good (hopefully) habit. A teacher can be of help if you ask him to immediately point out when you did smething wrong.