Don’t line your group up in a long row, squaring them shoulder to shoulder. For starters, it’s an unnatural way to stand and will make people feel silly.
Second, the results will be that your group photo looks like a criminal line-up.
Try to cluster everyone together nicely. Tall people should stand behind those who are more vertically challenged. Likewise, those who carry a little extra insulation will probably appreciate being placed behind other people (plan these arrangements in your own head, failure to do so may result in a broken camera or busted nose).
If you’d like to emphasize certain people, perhaps the hosts of the party or guest of honor, place them in the middle of the group. This will make them the focal point of the photo.