For Glo Bugs, I like to use a Mustad C67S, this is a size 12. I also like to use fairly heavy thread, here, 6/0 orange UniThread. Leaving some space behind the eye, get your thread started on the hook shank.
I like my Glo Bugs fairly sparse so I only use a single strand of glo bug yarn, about an inch and a half in length will do. A blood dot or a yoke on an egg always looks good so I'll add a single strand of micro yarn in a contrasting color. Stack both pieces of yarn and then fold them around your tying thread. Take a single turn of thread around the hook shank and pull the yarn bundle up to vertical. Now pull down the thread and give the yarn a little bounce to compress it. Take a couple wraps in front, behind, and then around the yarn bundle to secure it to the hook and compress it further.
You can then whip finish the fly and snip or cut the tying thread. Grab the whole yarn bundle and pull up. Then, with very sharp scissors, snip the yarn straight across. You can see how the yarn instantly flares into a half a sphere.
Although not required, I think applying head cement or, in this case, Hard as Nails, to the thread wraps helps the fly's durability.
With your fingertips, work the half sphere into a full sphere and there's your Glo Bug. As I said earlier, I like my Glo Bugs tied sparse, mostly so you don't have material blocking the hook gap which can lead to missed hook sets. Try Glo Bugs in different sizes and colors, it really is a remarkably effective pattern.