I've found that if you trim junipers by cutting them, the injured needles near the cut will turn brown. The only way I know of to avoid this is to pinch back the junipers by hand. This makes the wound occur between needles.

wider at the bottom so the sun can get to it and what dwobser said about the browness

We have a large ( 10feet wide x 6 feet high) Juniper in our front yard. It has some deadwood underneath. Should this be taken out or left. How much can a Juniper be trimmed - our is getting kinda large!

Junipers can be trimed at any time of year. 2 things that cause browning are,extreme heat or cold at cutting time, and shears or power trimmers that are not sharp. In either case it will flush out after a while. Dull shears rip the ends instead of cutting.
Frankzen you should remove the deadwood from below. You can cut as deeply into the plant as you would like,[you could get some crazy shape out of a plant that size!] as long as you still have green. Or blue or yellow or whatever colour your juniper might be.Hope this helps.