Self-portrait shooters usually rely on the trial-and-error method of focusing. Shoot, shoot, and shoot again until the perfect combination of pose, exposure, and focus are achieved. But there is a better way (several, in fact)! All of these methods are quick and easy and will give you accurate focusing without a lot of frustrating trial and error.
Before you begin, you'll just need to acquaint yourself with how to put your camera into manual focus mode. You won't actually use manual focus for focusing---you'll just use it to keep the focus once you've got it set just the way you want. For each of the methods below (except the last one), you'll auto-focus first and then set the camera to manual focus so that it won't attempt to re-focus when you take the shot. You'll also find that having a remote shutter release helps immensely.
Method 1: Avoiding the problem
If you let the camera auto-focus on your face while using a wide aperture, you'll probably find that your nose is in focus but your eyes are not. The solution is to avoid the problem entirely by using a smaller aperture. The smaller the aperture, the wider the depth of field, and accurate focusing becomes less critical. Use as small an aperture as you can get away with.
Method 2: Hitting your mark
Probably the most straightforward method, simply place an object (a stuffed animal, a pillow, a lamp) where you will be posing. Focus on that. Then pose where your stand-in is at.
Method 3: Reverse focusing
This is similar to the previous method except that you'll use your tripod itself as the stand-in. Since focusing is only concerned with distances, it doesn't matter if you are focusing on the actual spot your are going to shoot. All that matters is the distance between the camera and the subject. With that knowledge, take the camera to where you will be posing and focus on your tripod head. Mark that spot. This is where you'll stand for your portrait. Then put the camera in manual focus mode and put it back on the tripod.
Method 4: The string method
If you need super-precise focus with a narrow depth of field, tie a string to the tripod head and focus as above. Pull the string taut and mark it where it crosses the film plane (near the back of the camera where the sensor/film is). Anything at that distance from the tripod will be in perfect focus. Put the camera back on the tripod (again, set it for manual focus), find your mark on the string, drop the string, take the photo. Bonus: this method lets you shoot in any direction away from the tripod as long as you are at the focused distance mark on your string.
Method 5: Use a flashlight
Most modern cameras have a "closest-subject" focus mode. This mode will focus on the closest object it can "see." You can take advantage of that to auto-focus your self-portrait on exactly what you want. Using auto-focus, darken the room and shine a light on whatever you want focused, usually one of your eyes (but I'm not making any judgements---you shoot what you like). The camera will focus only on the illuminated object. Because the room will be dark, you'll need to use a flash.
Method 6: Measure
Measure the distance from the camera to where you will be standing and use the distance markings on the lens to manually set the focus. Not all lenses have distance markings so if you ain't got 'em you'll just have to find another way.
Other self-portrait tips:
- Put a mirror behind the camera so you can see the display without having to get up between shots.
- Use a cable release or remote. Even better if your camera can delay the shutter a couple of seconds so you can hide the remote.
- Be extremely awesome.
Photo credit: Zara