Every new forum needs to be noticed by it’s users to become success. Forum promotion is not an easy task. It need a lot of energy and patience.
Forum owners try different methods which they find useful to promote
Join in forum promotion website (like Forum Incubator) for post exchange is one way to get more content to your forum. Its useful for new forums as they will not have huge number of active users to fill some content. There are many websites which offer posting on forum for money.
Creating fake profiles in the forum to create a feeling of busy forum. Its useful for new forums. because people are interested in popular forums only.
Another way is keep the forum active by adding posts everyday to your own forum. New users will check the activity of forum before join. If they feel like the forum is of lesser activity, they will not mind joining..
What are the techniques you tried to promote your forum. Please share your experience