Yoz,
The first thing u need to do every time u start editor, is turn off all those options in settings, like auto camera and autosnap and stuff like that.
With auto camera off, u can be more precise. Also in edit mode, u say ur slection moves up and down a bit, check out the icon wich is a house with arrow in or ontop, try switching those and see what happens, the movement up and down is due to the raised/lowerd ground ur crossing with ur selection.
U should try out everything in a test map.
For instance , did u know u can draw a box in select mode to select every item in the box. When in selection mode, use unlock cursor then draw a box by holding down R2(I think) and moving the analogstick to draw a box.
I don't use snapping tools, when creating fences just turn autosnap on again.
So just try out stuff and u'll be surprised at what u can actually do
