I have no idea how to do this. Sometimes I pick up the yarn and it runs nicely, sometimes I end up with, say, 1 inch of length that just keeps getting shorter the more stitches I make and I must manually pull more from the ball instead of me just getting more yarn from the ball naturally with each stitch. ("1 inch" was just made up for this example, never actually measured it.) I have no idea what is affecting this. But the tension is awful and my practice piece looks like this. Please help me!
Try using different methods of working the yarn around your left hand. I have a "standard" method, but some yarns need more or less tension to run smoothly through your fingers, so I adapt.
Different material for needles, different types of needles maybe. I find it easier to knit evenly on circulars. Play around with needle size as well.
Another thing is your "inner tension". It's easier to knit evenly when you're relaxed.