For group shot, F4-5.6 is a good start if you are taking them head on.
Try to avoid diagonal lines where people are arranged obliquely away from you. If you really have to use F8 and above. To check dof, there is usually a dof button at the side of the camera lens mount. Pressing that will let you view in your ovf the actual dof you are getting.
Sweet spot for any lens is about F8. And anything that pushes F16 and above you may get diffraction problems. Sharpness will also start to degrade.
Assuming you are shooting in good light otherwise use a tripod.
If you are shooting in natural light, Lighting should ideally be in front of subject, above or 45 degrees to the side. Avoid harsh sunlight as that tends to make people squint.
If you are using a flash, try bouncing the flash onto white ceilings, above and slightly behind you if the subject is relatively close. Otherwise you may have tro project frontwards. Watch out for shadows under eye bags. Do balance your iso to get some background exposure balance. You'd want to aim for ambient exposure to be slightly darker than your subject. It also depends on what kind of results you want as sometimes people purposely blow out the background. Depending on the camera and flash that you own, you may have to bump up the flash output accordingly. Sometimes you may have to supplement outdoor shots with flash too. Here's where remote triggers and supplementary flash guns will help.
If your lens doesn't have enough dof, you may have to select the most important to be main subject. Focus on the closest eye. From what I found out, good light always increases dof and clarity. For instance, using flash seldom get me into trouble with lack of dof. I'm not really sure why.
Avoid unflattering angles. Always make your subject look good.
Hope these helps. Good shooting!