Taking self-timer self portraits with Nikon d3100 (or any SLR, really)?

Alright, so I'm new to the SLR world, and I just got the nikon d3100.
The other day I tried to do a self portrait, but the focus was always on the background.
how do I change it so that once I move into the frame, the focus will be on me, rather than the woods behind me?

Put the focus on manual and prefocus on the point where you are going to be standing.

Pre-focus, then set the timer. You can either eyeball it and test or focus on an object that will stand in for you while you focus, are about the simplest ways to do this.

That is good advice from the answers above.

You can also buy a nice under $20 remote shutter release and then you will not have to run from camera to pose in 10 second intervals.

You can just sit and press the remote shutter release button until you think you have enough shots

http://www.nikonusa.com/...ared).html

It is seeing way too much of what is around you. Get closer!