you have to look for which keywords you want to rank for. then make your blog and optimize it with techniques such as link building and meta tags. Then hopefully you can slowly get some traffic from link building and the search engine though search engine traffic comes later.
Well if Im opening a new site, what are somethings I should do?
for example, find your competitors, keywords, etc.
What should I do since im not that good with SEO
(1) Use the "seo toolbox" link in your signature to magically make your site perfect.
Or
(2) Build a good site and forget about SEO until you have a reason to be concerned with it.
Stick with wordpress - it's really good in SEO sense. All-in-one SEO plugin and xml sitemaps for starters. This just for basic SEO.. then starts the hard work of links and relevant content.