Learn to offer constructive solutions, first of all. Instead of telling someone their blog sucks, or that a post is lame, offer some specific suggestions for improvement. Help them get better. If you are going to take the time to make a comment, make it worth your time. Second, learn to interact with people in a more positive way it makes others feel good and it makes you feel better about yourself. And you can make some great friends this way. That's a good thing.