A few options:

You can take the Final Fantasy 6 approach: Lots and lots of characters, and the players have the option of swapping out characters are certain junctions. This can be dependent on your campaign, though. Perhaps they work for an army or mercenary company.

Another possibility is that you put together situations where the players take control of a completely different party. Perhaps it's a competing party trying to get that MacGuffin first, or a team of antagonists working for the BBEG. Or maybe it's just a prelude that the players will have the option of seeing from their unique perspective. For example, a team of characters invading a dungeon to get some treasure, but dying periodically throughout. A thousand years later, guess where the main characters find treasure?

I like option two the best. It gives your players a "main" character that they'll develop and be attached to (hopefully), but give them something different to break up the monotony every so often.