onpage techniques :
content
meta title tags
Meta description tag
keywords
H1 & H2 tags

offpage techniques :
directory submission
article submission
social bookmarking
blog
blog commenting
press release
classifieds

dofollow links allows search engines crawlers to crawl the link,

seo is process of optimizing the site for the particular keyword to get higher ranking & more visible in major search engines.

promote ur site to get traffic, do social bookmarking & submit ur site to social networking site i.e. facebook, twitter and to get higher ranking in search engine, use link building techniques i.e. directory submission, article submission, social bookmarking, press release, blog creation, blog c...

white hat technique is optimizing the website for the particular keyword using ethical ways i.e. Google's guidelines while black hat techniques is an unethical way of optimizing the website .i.e not following Google guidelines which includes spamming, hidden text, keyword stuffing etc.)

keyword density is the number of times a keyword is used on web page. it should be 3-4%.