Depending on what software you run, they may or may not have community developed addons/modifications/plugins that do part of the optimization for you such as dynamic meta tags, SE friendly URLs and so forth.
If it's a forum, don't bother. Just build content, a community and advertise.
If it's a blog, probably using Wordpress on a self hosted domain? Fix your URL's in the settings for more bot and user friendly, eg: "blahblah.com/category/postdate/postnumber" and change it to "blahblah.com/category/postname" etc. wordpress is fairly optimized already, Google trusts most blogs that provide good content and are on Wordpress so just keep the content unique and cooking, comment on other people's blogs in the same niche. Offer link exchanges, purchase links, advertise.
Never post up content that is posted elsewhere, maybe allow following on your blog comments to give visitors a reason to comment on your posts.
If your on a site, there is a number of things you need to do, create a capturing META description and Title that is both relevant and contains targeted keywords, make sure there is no duplicate content etc.
All in all, I wouldn't really recommend messing with anything until you read about what you are doing and research about SEO itself, people do it wrong and their site gets hurt badly, which is why companies and websites bring us in to do it for them 😉
Lastly, don't follow the crowd and be sheepish by thinking PR means everything, it doesn't. Forget about Pr and focus on converting.
I wouldn't worry about optimizing for SEO in the beginning. I would just recommend focusing on the content, later down the line you can optimize for SEO.
SEO starts from domain registration. My crypto niche forum has a domain name trade btc. Since there is a word trade and btc (bitcoin), I am able to attract targeted traffic.