Sometimes group portraits can be tough, but when you pose your models nicely and get them to interact with each other it can make a great photo.
The easiest (for me) to group is couples. (Whether in a romantic sense or just two people interacting.) There is so much you can do and convey when your models work well together and are comfortable with you as the photographer. It is so important to get to know your models and allow them to do what makes them feel most attractive and comfortable. As you can see below different people have very different styles. Some are fun and goofy while others go for the more serious vibe.
Larger groups are a little more tricky. You have to make sure that everyone is doing something that works for the camera and make sure that they are all focused. But as with couple portraits you can also get some great shots with big groups. Smaller groups are just a little easier to pose; in the photo below the snow really added to the group portrait to give it a cool feeling.
One great group portrait photographer is my professor, Nicole Nugent. Check out how she makes her models true characters show through in her group work!