How to take a self portrait with the Nikon D5100?

I'm new to the DSLR. I want to know how I can take self portrait that is a few feet away from the camera with the self timer. Every time I take a photo with the self timer further away from the camera the picture goes out of focus. How can I keep it in focus while still being away from the camera? Is my only option to buy a shutter remote?

You need a tripod
You need a remote shutter release (so you don't have to be continually running back and forth to take the next shot using the self timer
You need to set the cameras auto-focus to continuous, otherwise when you press the shutter release, the lens will focus behind where you intend to be sitting. This is good to do whether you are using a remote shutter release or not
Some kind of stool to sit on. It will mark the place where you will want to be during each shot. Otherwise you may or may not be in the frame of the camera

Remember to shoot with the camera in the portrait (vertical) position for your head and shoulder shots

Imagination and resourcefulness are two things kids sorely lack nowadays. Not all solutions require buying something. I'm glad though that at least there's one less picture in the internet of a kid missing an arm to the edges of the picture.

Set a chair on where you will be standing or sitting. Let the camera focus on that. Lock focus by switching AF off (go to MF). Set self-timer, press the button, then run into position. If you will sitting then sit. If you will be standing then kick the chair over and stand in its place. Repeat until satisfied or when foot is already sore.

For a sharper focus, let a broom stand on the chair and focus on that. The broom is lighter and will not fight back when you throw it so you will be able to take more shots without your foot swelling.

You need a tripod and preferably a remote. That simple.

Focus on something that's about the same range where you plan to put yourself. Lock the focus, use the self timer… Voila.

A few feet away is too close for portraits. You will get unpleasant wide angle distortion - not a good look!

1. Get a tripod, tilt the camera side on (portrait orientation).

2. Set the camera up a fair distance from the subject - as far as possible - use the camera's zoom lens to frame the shot (assuming you have a zoom lens) or something like a 50mm lens. You may need to pre-focus on a target, which you can replace yourself with - if there's another human being present, it would be handy! If your camera has a continuous auto focus mode (or servo mode) then it shouldn't be necessary.

3. Shoot in diffuse lighting, not direct sunshine, avoid on camera flash. By a window is a good location.