If you do only five things:
1) Keep it simple and focused. Focus the persona on the design task at hand, not the target user’s entire life story. See what you can do with one page and at most two hours, using the facts that you already know. Anything beyond that is detail you won’t need anyway.
2) Make a user model, not a life story. Just give that specific facts to help make good decisions. If there’s not a potential design decision behind the detail, don’t include it. Don’t walk a mile in the person’s shoes. If your persona looks like an online dating profile, you are doing it wrong.
3) Use them when making decisions! If you aren’t actively using your models when making design decisions, you’re doing it wrong. And by “actively using”, I mean applying the model not making arbitrary assertions. Flag assertions that are outside the model and validate them.
4) Train your team to use a simple process. Give some simple training on how to use personas productively. Don’t assume that people will figure it out on their own—my experience shows that they won’t.
5) Be mindful of politics. If you can’t use personas for political reasons, just call them user models. If it helps, consider calling them “agile user models.” Most likely nobody will catch on.