Front to back is done by raising or lowering the jockey wheel, side to side needs a ramp under one wheel, unless its a long way out I don't bother with the side to side bit.
As to where to put the level thats a matter of personal preference, I usually put mine on the awning rail .............. saves me having to keep going in and out to look at it.
As long as its somewhere near it does not have to be perfect.