Make a list of around 10-12 forums related to your niche and post in them. If you have a health site than hang in health forum and you can link back to your related content at appropriate positions. For example, you can use Adobe’s community forum to get links and traffic if you have a photoshop or design website. This is just an example, don’t even think of spamming there.

Some of the Middle size forums are more appropriate for your site promotion since they are way more generous in rules as compared to bigger sites.

Use "your niche + forum" and such key phrases to find relevant forum.

I will try to add more pointers in this section later, you can also share your tips/softwares/tools with others here as a comment.