What, just ordinary habits/behaviors/actions that may carry unintended, negative consequences?

Smoking weed improves your odds of becoming lucid (or so some claim...I'm not prepared to back up or defend that claim), but tends to wreak absolute havoc on your recall.

Staying up too late/not getting enough sleep can halve your odds of becoming lucid.

Obsessing over lucid dreaming can be negative, too. If it is all you can think about, etc, you'll actually be hurting your chances. The thrill wore off after about a month for me. Sooner the thrill wears off, the sooner you can start doing some serious lucid dreaming.

Those are the biggies that I know of...