Know your role. It's terribly difficult for some women, myself very much included, to stop tending to the needs of other people once we leave home and get to work. But while I live with small people who actually need me to help them solve life's problems, I work with big people who can solve them on their own.
Establish clear boundaries. All women, married and single, need to be wary of tip-toeing across the line that divides professional and personal relationships. That means no talking about marriage (his or yours), non-work related insecurities, or anything else that feels like it belongs in a more intimate relationship. And even when we know everything's on the up and up, we need to be aware of how a friendship with a male co-worker might look to others. Limit one-on-one meetings and always, always, always, keep the office door open.