Toss

Basket Toss (right-hander eg.)
Doesn’t have to be a basket. Can be a little ball tower (1 ball balanced on 3 balls.)
Get into the Checkmark (or partial checkmark as a progression) position. Racquet is up. Elbow is back.
Full checkmark has elbow in line w/ the shoulders. Partial checkmark could have elbow somewhat left of the shoulder line.
Toss the ball up at least contact height (arm extended up) and try to hit the target.
Left foot is touching the back left corner of the basket.
So the basket is in front of the player, but a little to the right.

Toss + Catch
Simultaneously take racquet back into the checkmark, and toss the ball up.
Catch the ball w/ the tossing hand.
Catch the ball w/ tossing arm fully extended up.
You should feel at stretch under your arm.
Do not move feet.

Toss + Catch Pre-Checkmark
Take racquet back into the checkmark.
Slightest of pauses, and toss the ball up.
Catch the ball w/ the tossing hand.
Catch the ball w/ tossing arm fully extended up.
You should feel at stretch under your arm.
Do not move feet.

Something on your Head
A face cloth or a paper cup …
The idea is to keep your head still.
And also to not swing the arm up and behind you.
Balancing the object reinforces that.

Just Fingers
Hold the ball w/ your fingers, not your palm.
As you move your arm up, open the fingers, like releasing a butterfly.
This limits the wrist flick problem.