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. The entire plan doesn't have to take nearly as long as you might imagine. 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.
A 'terms of service' or (TOS) page is the most important page to read before you begin marketing on your forum. This is where you'll find out what's acceptable so you can enjoy a long and profitable relationship with the site. It's never wise to violate a forum's TOS. Doing so can get you banned from the site for life. They generally aren't concerned with whether or not you actually read the TOS. If you violate a TOS, then they assume you've read them and violated it anyway. This is how they see it, at any rate. If you're planning to market on the forum then you need to know and understand the terms they've established for doing so. Anytime you sign up for a new forum, you should look around, and specifically search for a couple different things. You need to think about why you want to join this forum, which can be determined by looking around. You have to consider some things since you will be using the forums for your online marketing. It is typical for online marketers to be shunned at many forums these days. In most cases, online marketing won't occur because the owner won't let you. You can sometimes find that out by reading the forum rules. More than likely, if there are not any links or signatures at the bottom of each post, then probably not. Regardless of the type of forum, direct advertising is usually not allowed. They are preventing a billboard effect from taking over their forum by not allowing ads to show up.
Any time you join a forum, you have control over your own persona or how people view you. You can create whatever character that you want to be. But do this with caution because you never know what will happen. If you have a strong personality, then for example you can tone it down from the beginning and keep it that way. A lot of people just are not as aggressive. But, this all depends on the viewpoint that others have of you. According to your subject matter, you may want to remain in the background only. So, remember what you want to accomplish when dealing with all of this. It is possible that, after reading this, that you may already know most of what we have discussed. It's all about using common sense, and abiding by the rules that each forum will inevitably set up. Be a good see this site community member and that will take you most of the way.