Mark the end of the week, and make room for socialising. Returning events and traditions feels secure, and make room for getting to know each other better, which again just makes it more fun to go to work.
A birthday is a special day. Remember to mark it. Decorate the office a little (or a lot), or make other traditions, such as singing a birthday song, special hats, something sweet to the tooth, or whatever.
Never miss. Always nice.