I have been struggling for years to get my portraits in sharp focus, and I FINALLY figured out how to do it.
1. You MUST USE A TRIPOD!
2. Sit one of your subjects down and don’t let them move. Set the focus to manual (on the lens) and adjust until it looks good.
3. Take a practice shot then view it on your camera.
4. Zoom in close and see if the photo is still in focus. If the photo is still in focus zoomed in, it’s tight as it can be and you’ll be able to blow it up without any problems.
5. Don’t move the camera! Make sure your aperture is small enough (a big enough number because it’s really a fraction… 3 – 4ish something is usually good), arrange everyone else in the picture, and shoot away! Really go to town, you can never have too many…
If you get that one person in focus and then don’t move your camera or that person and arrange everyone around him/her, you’ll be good!