Get multiple followers
First find any follower
Serana preferred
Then do a quest that requires someone to follow you
Then do a different quest
Then rinse and repeat, its possible to have quite a few people with you currently i have 5 people with me storming a forsworn camp
(Karthspire) and im looking at it all it looks like an all out war and ts awesome

Good tip for console players

PCers (like me) can use the UFO mod to have several dozen followers at a time. I took about 8 one time and turned them into werewolves (used a werewolf mod) and tore across the countryside... epic.

Why didn't i think of that o.O