Becoming a popular member in online forums is not so tough. Only few things can make you popular.

1. Emphasize on creating ‘Thread’ rather than ‘Reply’. You are always on top, because you created the thread, so each and every reader reading your post. No matter how many replies that thread got, you will never go to last.
2. Reply to the latest threads, so that all the readers can find your post in top.
3. Write posts in easy words, so that all reader can easily understand what you are saying.
4. Add a better profile picture/avatar.
5. Never copy paste others threads/replies.

6. Keep good relationships with other members by giving them reputation for good writings. They will also do it for you.

All these can be your key to be popular on online forums.