Does your knitting show a significant jog or stairstep at the beginning? It's caused by joining the first round of knitting to the cast-on round. What you really want to do is join the cast-on round to itself. A good way to do this when using a long tail cast-on is to use the "Wag Your Tail Jogless Join."
Set up for long tail cast-on with tail going over the thumb of your left hand and working yarn going over your forefinger. Do not make a slip knot. Instead, insert the needle below the yarn and hold the yarn to the needle with the forefinger of your right hand. Then pull back and cast on a stitch. You should see two stitches on the needle. The first stitch is not very impressive. It is more of a loop than a stitch, but that's just what you want. Snug up that first stitch a bit so that it's a little tight.
Continue casting on the required number of stitches. Arrange the stitches for circular knitting.
Instead of knitting the first stitch with the working yarn, put the working yarn down and pick up the tail. Give the tail a little wag for luck and then use it knit the first stitch. Transfer the just knitted stitch back to the needle in your left hand.
Turn your work over. Take a tapestry needle and thread up the tail. Then find your working yarn and follow it all the way up to the purl bump and insert your needle into the purl bump from below and pull tail through. This completes the "Wag Your Tail Jogless Join."
Turn your work over again and pull on the tail a little to tighten up the join a bit. Add a stitch marker to the right hand needle. Pick up your working yarn. You are ready to knit the first round. The stitch you made with the tail is considered part of the cast on. Therefore, you will knit it again as the first stitch of the first round.