|If it's cloudy today, consider yourself lucky! Otherwise, face them with their backs to the sun and use fill-flash, so they don't turn into sillohettes. Probably a low ISO is fine (100 - 200).
How many people? Try scrunching them together and staggering them in maybe three rows - sitting, kneeling and standing. If it's a big group, I've heard that some great shots can be taken from above the "crowd," so maybe a step-ladder is in order.
Other than that, maybe have everyone facing toward one another (left facing in right and the right facing in left. They can get closer that way as well, so that you can get a tighter crop.