Recently, my girlfriend of about a year started a new job, which is great, except that it makes her my boss. Things have become really awkward between us, and I don't know how to talk to her about it. What should I do?
She's the Boss
Talk to her the way you would talk about anything in your relationship. Make sure you're not on the defensive leading into the conversation and don't start with, "We need to talk," since that never puts anyone at ease. Instead, try asking about her day, or asking about the new job more broadly, and then listen as much as possible. She's probably just as uneasy about the situation as you are and will be relieved that you're taking the lead on getting things out in the open. See if you can find things about the predicament to laugh about, and then be sure only to laugh about them at home and not at work. Tell her that you value your relationship, you're proud of her promotion, and you want both parts of both of your lives to be successful and fulfilling.
You also need to make sure that her bosses know that you two were in a preexisting relationship because otherwise her job (and possibly yours) is potentially at risk. There was just an episode of Fairly Legal about this, and while I doubt your place of employment would try to cover up a government scandal by firing the both of you, there can be serious ramifications to undisclosed workplace romance. You'll also need to figure out how to negotiate the relationships with your co-workers who may be looking for cases of preferential treatment from the boss. Do your work well and responsibly, and don't give them any fodder for such claims. Hopefully this goes without saying, but never show any PDA at work and don't talk to your co-workers about your relationship.
Since you and your girlfriend will be seeing so much of each other at home and on the job, it's important that you also spend time apart. Go out with separate groups of friends occasionally and pursue individual hobbies and interests. Try to avoid work talk as much as possible when you are together. If you need to vent about work, talk to friends who are not co-workers or mutual friends.
Finally, if your relationship continues to feel awkward and you decide it isn't working out — whether the job contributed to that or not — one or both of you may need to find other employment. Give yourselves time to adjust to these new roles first, though, and hopefully your relationship will be able to withstand the pressures and emerge stronger for having had to figure these things out!