Bride
Groom
Best Man
Matron of Honour
Parents of Bride (or whoever gave you away if father not present)
Parents of Groom
Priest/ Vicar/ Minister- if its a church wedding
Some of the big weddings I've been to have had all the Bridesmaids and Bridegrooms on the top table too.
Families are always up front, in front of the top table- most immediate family closest
Don't run the risk of leaving people to sit where they like- doa seating plan- the whole point of it is bringing people together- it stops that random Auntie or family friend being stuck on her own not knowing anyone... or worse, your Auntie and Uncle having to sit at seperate tables because in cafeteria fashion, theres only tables left with one space on them.
Put people together who you think will get on, have something in common.
Usually immediate family (brothers sisters, and pageboy/flower girls are all sat together- either at 2 seperate tables or at one table if both families are small)
The other tables are usually mixed- in a man, then woman fashion, with friends and family mixed around the tables so they are mingling. (but not stranded with no-one they know)
When my brother got married, he invited some of the 'lads' he worked with and their girlfriends- and sat them all together, so they would have more fun, and it wasn't so important for them to meet family members)