SEO is a complete game of keywords and if you choose wrong keywords then your all work is waste. So you will choose any good keyword tool and use it for target the right keywords. I use Google adwords Keyword tool for select the keywords for my website. After choose right keywords follow all search engines rules and websites rules where you post your links. Try to avoid Black Hat techniques like Spamming, Cloaking and Keyword stuffing because no any search engine allow it and if your website will caught to use it. your website may be ban or penalize.
Black hat SEO is bad in long term but we can't deny that it's still very popular. In my place, there are some forums that are just dedicated to discussions about black hat techniques.
Cross links means here - Websites hosted on the same IP linked with each other. Also few more points should be in the mind of seo's :
-- Webpages should be light, donot use heavy images, unnecessary comments in the pages. Use CSS and optimized images to reduce page size.
-- Hosting plan is also very important. Choose best hosting company to host your website.
-- Register your website in google webmaster. This is give you useful information about your website including keywords, sitemap submission 404 not found page information. Immediately take action on 404 not found pages.
-- Donot use or avoid duplicate content from your website. After the updation of Google Panda, duplicate content will harm your website.
Yeah, The Google Algorithm is very hard to understand.