Doing it away from the wall is scary at first. I kept falling backwards.
Look at this video and website to see if it helps.
http://www.sivananda.org/teachings/asana/headstnd.html http://www.expertvillage.com/video/56272_sivananda-yoga-headstand.htm
The important part of the video and the instructions is
1. to measure the space between your elbows and make sure its the same as it would be if you had each hand on the opposite elbow. If it’s wider it’s harder to keep steady.
and
2. to try to just bend your knees up at first—this is the secret to not falling over. For some people this is the hardest part because your back has to be pretty vertical for you to come up this way, but if you can get to the point where your back is straight and you use your stomach muscles to bend your knees and pull your legs up (it’s sort of like you are kneeling while on your head) then the rest is not too hard.