When casting on to circular needles is there a technique to not making it too tight or too loose? I realize the first row after casting is hard, but I've really struggled casting on partly because the loops on the needle part are super loose but the loops, when they end up on the cable part of the circular needle are very loose. (If this is too vague or confusing please let me know)
Getting a circular cast-on up and running can indeed be tricky. Fortunately, there are several techniques that can help.
Use a sturdy cast-on The long-tail cast-on is a good one for this as it basically includes the first row of knitting. Be careful if you need stretch, though.
Add some weight to the cast-on This can be done by putting some stitch markers in the cast-on (helps get the number of stitches right, too!) or by knitting a short provisional section flat and then joining (you go back later, unravel the provisional section, and use that yarn to cast-off).
Try DPNs If the cable part is what grieves you, you might try casting on with double-point needles, instead. They can have their own fussiness, but it works for some folks.
Practice Yeah, nobody likes to hear this one, but it's so very true. Even after more than a decade of knitting, it still sometimes takes me a few tries to get a circular cast-on going well.
The looseness or tightness has some effect from how close one cast-on loop is to its neighbor. I tend to cast on too tightly and have sometimes held a circular needle together with a narrower double-point. If experimenting with where you place each loop doesn't change things, you might cast on to a smaller needle than you use for the rest of the piece.