Knitting in the round can seem daunting, but with a bit of practice, it’s no more difficult than knitting on straight needles. Here are some tips that I hope will make it a bit easier!
The appropriate circular needle length is the same size or slightly shorter than the circumference of the piece you are knitting. If it’s too short you’ll have trouble keeping all the stitches on the needle; if it’s too long, the fabric will be stretched too taut (this is why you need to switch to double points when decreasing the crown of a hat).
For some people, the usual way of knitting the first stitch of the round can be loose and therefore sloppy. You can tighten it up with the tail when weaving in the end later.
A better way to join it the round can be to cast on one extra stitch. Slip this stitch to the left (the first needle if casting on to double points); this is the beginning of the round and next to the first stitch you cast on. Then knit the two stitches together.
Still better, slip the first stitch you cast on to the right, next to the last cast on stitch. Pass the last cast on stitch (which is now the second stitch on the right) over the slipped stitch, give the yarn a tug and begin your round.
Aluminum needles can be slippery and your stitches will always want to slide off. Try bamboo or plastic.
Double points come in different lengths. Longer ones can be a bit more awkward but for larger number of stitches, you’ll need them so your stitches don’t fall off.
They come in sets of 4 or 5. If you have the option, always buy 5; then you’ll have it if you need it (and if one disappears you’ll have a spare!).