Make sure the stitches aren't twisted and then with the working yarn coming off your right needle start knitting.
A 16" needle (measured tip to tip) is the best size for a hat. If it's too large you'll need to do magic loop or modified magic loop.
Here's the KH video for knitting in the round.
And another site with good pictures and it shows you the proper way to hold the needles so you're not knitting inside out.
Tip: knit a few rows before joining..it helps keep the stitches from being twisted. If they twist you have no choice, but to start over.