Susan52 has some excellent tips on doing just that.

How do I keep my lens fresh?

Susan recommends interactive modules to “get visitors involved” and I find this one tip invaluable. I get that poll module on every lens I make. Sometimes, I create the lens and come back the next morning to add a poll. I like the duel module too, most lenses can accomodate one of these.

All in all, she tells us six quick ways to update a Squidoo lens.