I bought some clippers last summer. I like trimming my own hair, though I usually don't go lower than 4 or 5. It just takes a little practice. What I've found (for me) is that:
-It cuts easier with wet, freshly showered hair.
-It's more effective to cut "against the grain" so to speak, that is when my hair is long it leans in a certain direction, so I cut against it (front to back works well for me).
-Cut standing over a toilet to save on cleanup.
-Once you think you're done, comb or brush your hair as upright as possible. Check for evenness and trim as necessary.