So my teacher pointed out the other day that when I play, I tend to flatten out my finger at the first joint (the joint closest to the fingertip). I seem to mostly do it on scales or passages where I am playing on a lot of black keys (probably because those keys are farther back). Is there anything in particular I should do to work on that (aside from just noticing it), and should I try to move my hands a little closer to the black keys?

Note that my whole finger isn't flattening out, just the part nearest the tip.

I tried to do this, and it was nearly impossible for me without flattening the second knuckle.. however, I did notice some tension in my hand while trying to pull this off. I think it's going to be a lot of slow practice, making sure you aren't holding your fingers "locked" over the keys you need to play, and making sure you properly "shape" your hand (and each phrase) so that you hit each note more naturally. This is a relatively new one for me, so I really can only offer general advice unfortunately.

Are you sure you don't mean to say that your first knuckle collapses? Meaning that it bends backwards slightly? That is a more common problem, so that's why I ask.

That is probably what I mean, I'm really sure how to describe it!

Check your hand position. When performing runs / scales, we need to move our hard a little closer in so they fingers can be close together whether they are on black or white keys. Your fingers will more naturally curl in that position.

For arpeggios we tend to move out and flatten the fingers a little.

Often this problem of a collapsing knuckle is, rather misleadingly, known as finger strength. Scales are good exercises as is, some people hate it, Hanon.

Ah, okay! In that case, you probably need just a little more firmness in your fingers to prevent the knuckle from collapsing. Play a little closer to the tips of your fingers, instead of back on the pads of your fingers. Press down into the keys to get the feel. It should be *nearly* impossible to play near the tips of your fingers while pressing down into the keys and still have this problem. If you try it, you will notice that it should feel very wrong.

Let me know if that helps. There are other "tricks" but I like to start with the easiest fixes first and see how they go.

When I play a black key after playing a white one, my hand goes up and towards the black key. Then my finger is hanging nicely above the black key. When I drop my hand, the sound is much better than when I play the black key with the hand in the same position as I would have done with a white key.

But with fast passages with a lot of black keys I don't know how to move the hand though. There isn't time enough to move the hand but sideways. So I play the white keys as if they were black keys, with my hand high and forward. Playing my thumb almost vertical.

There is an excercise for violin players to strengenth the curved position of the fingers. Lay your handpalm flat on a table. Curve your fingers as much as possible with the fingertops vertical on the table.

I extended the excercise with moving fingers up and down, one at a time. Still being in a curved position. Because I sometimes have a difficulty lifting up finger 4 in wide chords.

I wouldn't isolate your fingers like in the exercise you described. The fingers are largely meant to move together with the hand and arm. Isolation creates tension instead of strength. If you can grip a water bottle without dropping it, you have all the strength you need to press the keys down.

You are correct that your hands need to move in to play in the black key area. It's difficult to generalize this, however, so I'm not sure how helpful I can be without discussing something specific like a particular passage.