The best place to put the camera is on your lap. If you can put a magazine or something on your lap - that can help a lot. You can adjust the up/down angle by going up on tips of your toes - but that'll kill you if you try to do for too long.
Of course, the best way to shoot is with the LCD window open - but that'll also get you busted really quick. However, a neat little trick I picked up from a very experienced filmer: get a piece of the plastic used for window tinting and cover your LCD monitor with it (tape it on all four sides). Use two sheets if it's not very dark. That'll reduce the light signature dramatically - but you'll still be able to see what's happening on stage.
But the safest way is to use the normal viewfinder. Let's face it - a static shot of the stage sucks big time. You want to zoom in/out as appropriate. The way you do it is simple: get to know your viewfinder. It's not as hard as it sounds. Turn on all of the available viewfinder options (battery life, timer, etc., etc.) and know where each is positioned on the screen. You can also use the green recording light. On my cam, the green recording light is top center. The timer is lower left, just left of center. Of course, all of this is assuming you have a camera that you can set on your lap and still look through the viewfinder. Can't do that with a Sony HC-21 because the viewfinder doesn't adjust up or down - it only extends outward.
But getting back to looking through the viewfinder... if you know the green recording light is top center - just take a peek into the viewfinder and zoom in and frame the shot so that whatever you want at the top of the picture is just below the green light. For example, if you zoom in on the lead vocalist - do it so the green light is right at the top of his head - and voila - you've got a nice shot.
Like most things in life - practice makes perfect.
