When knitting in the round, there is often a gap in the very first round of your knitting. So, use your yarn tail from the cast on to close that gap for a smooth even appearance.
General Method to Close Gap at Cast On
Thread tapestry needle with yarn tail and go into the loop at the base of the last stitch in the first round. Then go into the base of the first stitch, forming a figure-8 and pulling gap together. Rep figure-8 until gap is fully closed and filled. Then work in tail.
Close Gap When First Row is Worked Flat
Thread a tapestry needle with the yarn tail and go into the loop at the base of the last stitch in the cast on. Then go into the base of the first stitch, forming a figure-8 and pulling the gap together. Repeat the figure-8 until the gap is fully closed and filled. You may need to seam the first and last stitch of Row 1 if there is a gap. Then work in tail.
Closing Gap at the Bind Off
Before cutting the yarn and pulling through the last stitch, you can close the gap by putting your right needle underneath the loops of the very first bind off stitch and pulling a new stitch onto your right needle. Now, bind off that last bind off stitch, cut the yarn and pull it through that added stitch. Then work in tail.