I responded to a "choosing friends" question in a another thread. Someone recommended that I actually post it as a topic since there are many new people to MFP in this group--plus, I think it's good advice:

One of the best things to do to encourage someone else is to "friend" them. But don't just stop there. Take the time to encourage them, review their diaries or offer a daily word of encouragement. Remember, part of the challenge to to "encourage" at least 10 of your MFP friends daily.

A word to the wise: On MFP you tend to have friends and then you have FRIENDS (associates vs true friends). Recommend you look for three types of friends: 1. Those who are where you want to be: These are the friends who have overcome the types of obstacles you're currently facing (e.g. losing large amounts of weight; fighting diabetes, etc.). Learn from them; 2. Your peers: People who are in the same boat as you. People who are in the same fight. Encourage them; 3. Those who you can help: People who need help iin a variety of ways (e.g. diet, exercise, hope). Teach them.

Your list should be a balance of the three.