I take it as you haven't had much experience in usin' Hi lifts. I'd suggest tryin' to have some buddy who knows how to use these things to demonstrate and let you practice on gravel road or something similar (pavement is really "unstable")
At least read lots of info and be cautious. You can't buy a new head in the next hardware shop, unfortunately, otherwise I'd be alot smarter.
The thing you need to be the most cautious 'bout is NEVER GO UNDER THE RIG WHILE STANDING ON A HI-LIFT JACK UNLESS YOU CAN SECURE THE VEHICLE FROM FALLING ON YOU!!!!! This cannot be practiced enough, last year two guys died from similar situation, 'cept they were usuin' forklifts... and not hi lifts, but this is even more critic with the hi lift as it can be extremely unstable...
#1 the hi lift can be unstable
#2 It can slip from it's seat, or the ground beneath it can be slippery
#3 the Jack always pushes towards the vehicle. (unless in an odd universe) so keep the foot abit on the inside of the vehicle, the more you need to lift the more you have to put the foot inside.
#4 It can swing to left or right, if you feel it's goin' abit too much in either direction, just loosen it up and relocate.
#5 Be careful, the whole weight of the vehicle is sitting on that little jack (ah well, part of it, enough to break bones at least) so be careful when raisin' it and lowering it. The shaft can smack your face, SO KEEP YOUR FACE CLEAR FROM THE HANDLE. ( I do know this from bitter experience)
#6 Be cautious and be aware of your surroundings, the truck can slip while you are raising it and fall off the jack. If you are afraid of hurtin' your beloved ones, tell them to keep an safe distance from you.
#7 Use some gloves. It's usually a better grip you get. Preferably leather.
Hope this clears abit up. Just be cautious and don't do anything you might think you'll hurt yourself. And also, take a few tries on the jack in "safe zone"
If you need more detailed info you can pm me..