I just started a new forum dedicated to skin health. I want this forum to eventually rank when someone Googles "how to treat dandruff" or "how to treat acne." What should I do to make it so my forum ranks high in the search engines when people search for these keywords?
Just keep adding lots and lots of really specific content about health conditions. Using the phrase, how to is also a good idea as most people will use that as part of a search query. Also, it might help with your mobile search audience.
Just think of all the possible things a person might want to know about skin health and provide really high quality, in depth content to answer their questions.
As for backlinking, be sure you only get backlinks from the most reputable skin/beauty related resources (forums/blogs).
Get backlinks to your posts and inner pages, not just your home page as you want to rank individual pages so they will appear when someone searches on Google for, 'how to get rid of dandruff', etc.
A good way to do it would be make the phrase appear in the title tag and an in the meta description of your website. Another good strategy which I recently learnt about is the anchor of the text links. Use the phrase you want to rank for as the anchor text when linking back to your website. But make sure that not all the back links are the same phrase as this might get you penalized by Google.