To pack the hair tighter, you need some sort of hair packing tool, finger nails are too flexible and you will get very sore finger tips as well using your nails. An old pen barrel works rather well for this and it is far cheaper than buying one of the commercially available packers made of brass or wood.
Use a good strong thread, my favorite is Danville's Flat Waxed Nylon, and use a bunch of hair that is between a pencil and your little finger in diameter. For all but the bunch at the butt of the fly, cut the tips off the hair just before tying and spinning it. Spin the hair on a bare hook is at all possible because this allows the thread holding the hair in place to slide on the shank and thus the hair gets packed tighter. Also, use a flexible cement such as Dave's Fleximent to hold the thead and hair in place after it is spun and packed. Just put a dollup of cement of the hook where you are going to spin the hair, then spin the hair over the cement.
Also, when spinning hair, place two loose wraps of thread over the hair bunch and then let go of the hair as you wrap the thread around the hook. This allows the hair to spin and it also results in the hair being trapped by the thread in different places as you wrap. don't stop wrapping until the hair bunch stops rotating around the hook.
At the head of the fly, the last two bunches should be not more than a pencil in diameter and packed after each one is tied and spun. It will look like the hair is over the hook eye before either of these last two bunches are packed. After the head bunches are tied in and packed, hold the hair out of the way with your left hand and whip finish the Flat Waxed Nylon.
Tie all of the flies before trimming any of them and then go at them with curved blade scissors to shape them. Dave's Fleximent is better to stiffen the face of the hair bug than head cement because it remain flexible.