Whether you have the extended family assembled for a visit, or just your immediate family, my approach is pretty laid back. I like to see where things will naturally fall before I start tweaking things.
I think that everyone naturally falls into a good place on their own as long as I tell them where to stand and then tweak a few things. I have found that when I give too much direction, people get awkward!
I also like to do different groupings within extended family groupings. It's really fun to look back at these!
And I also like to encourage people to just have a little fun. Your personalities are fun and deserve to be captured!