We often make great friends at work, there are several instances where people have found their one true love in a colleague. It is only natural to bond with people we spend so much time with. However, we must always keep the personal away from the professional and not let our relationships affect work.
Here is what we can do:
Keep space between your work and friendships
Distinguish between work and friendships at office. Do not discuss project details with your friends unnecessarily. Such discussions do not belong in your personal space.
Do not encourage gossip
Your friends may have news/rumours about your other co-workers, stay away from those. You do not want to colour your judgement with these. Your colleagues and teammates should not be affected by what your friends think of them.
If your friend is part of your team or if you are his/her direct supervisor please be careful of subconscious positive bias. Be fair in your treatment of all team members, your personal relations should not weigh in here.
Sure you have friends, but do not exclusively hang out with them while at work. Other colleagues should not feel alienated or left out.
Keep these in mind and work will be fine. Post work enjoy a drink with your buddies, play a game and relax as you deem fit.