I use a track pad on a computer. The key is very quick and confident lines. Dont worry if you make a mistake, just make sure it goes in the general direction you want it to go to and adjust it.

Either way, the key is quick and confident lines. It doesn't matter if its a mouse, a touchscreen a pen etc... quick and confident.

Actually, you don’t need to zoom in very far at all! The normal zoom is fine, the point is to make one quick and continuous line. The smaller the line is the harder it is to smooth it