Lots of things will affect the tightness of a knitted stitch. These are the ones I see people talk about most often:
- the knitter’s experience
- the knitter’s mood
- the kind of knitting needles
- the kind of yarn
- the style of knitting: Continental, English, Portuguese, combination, reverse combination, Eastern crossed, and so on.
- knitting flat or in the round (less likely to be a factor if you use either kind of combination knitting)
There’s one factor I don’t see mentioned as often, though certainly it does come up on occasion. I just think it’s worth highlighting: the final factor in how tight a stitch will be on the needle once it’s made is not how tightly the yarn is wrapped around the needle while working it. Rather, it’s how hard the knitter pulls on the yarn between knitting one stitch and the next.
Changing that tension much isn’t always feasible, but I think being aware of it can be a help. There are also times it can be important to make use of it on a conscious level. For instance, I find that I have to give an extra tug after knitting and then passing slipped stitches over to keep the decrease stitch from being much looser.