Trying to develop a cordial friendship with someone you were actually in a relationship with is a very different scenario. There are usually negative emotions lingering post-breakup. Hurt feelings and anger can make a situation very uncomfortable. While avoidance is not the answer to making the post-hookup less awkward, it may be helpful when emotions are out in the open. Right after a break-up, or even at the beginning of a so-called break, space for both people is the most important thing. This means that even if you are ready to move on and are comfortable being with the other person, they may not be. You should allow them space to get over the relationship.
Respecting their space can be difficult because this may cause you to miss time with your friends. When you are part of a couple that breaks up, the repercussions should never be diffused to your respective or shared friends. That will cause dialogue about the relationship and breakup and cause all the bad memories to linger. The next step after giving the person space would be to become cordial with him or her. The best way would be to casually greet the person next time you see them. If that goes well for an extended period of time, then it is smooth sailing from there. Remember, time heals all wounds, and in many cases a friendship is possible if you both want it.
Harboring bad feelings toward someone you were once intimate with is never good. In order to avoid having uncomfortable interactions with someone who you have hooked up with, be outgoing and friendly to them. On the contrary, when ending a romantic relationship, especially a long term one, giving the other person room to breathe before reintegrating him or her into your life is best for both people.