Every niche has many forums dedicated to its discussion. All that's needed now is to find the forums that get the lion's share of the traffic in your niche so you can put your plan into motion. That may sound like a very long time, and if so then maybe you believe all the sales letters. But if you want to get maximum value from your efforts, it will require some time and patience on your part. It's up to you what the best choice might be.
Most people, maybe everyone, behave in forums according to their general personality. Some are more aggressive and outspoken and others are shy and reserved. So, unless you are a rude person, just be yourself. If you are shy, it is okay to just watch things before you start contributing. This is a common activity called lurking. It can feel a little daunting to make your first post, and it's a lot like being in a new city or town and going to a new school. Just post in other threads and add something to the conversation.
A easy way to determine if marketing is allowed is to look at the signatures. Confirm whether or not the signatures have links in them. This is how it is done if forum marketing is not frowned upon. When you start to frequent plenty of forums, you will be able to determine what the members can do in terms of marketing. In addition, you can pretty much tell what you can do by studying the signatures of other members. For instance, you can often see multiple links with graphics, etc. This will show if a forum really likes people to market their goods and services.
When you sign up for a new forum, you will have the freedom to tweak your online presence. You can choose to be anyone you want in terms of personality. But do not get crazy with this because you cannot predict the future. If you tend to be loud, you can stop this and do not do it any longer. A lot of people just are not as aggressive. But the main thing is based upon how others view you. Based upon your subject, you might want to remain unknown. So you may want to think about this depending on your circumstances and what your goals are.
I've seen very many people become addicted to hanging check my reference out in forums. Whether or not they're getting a lot of marketing done is another story. Don't lose sight of the value your time has and where it would be wisest to invest it. You want to get the best possible Recommended Reading value for your time.