Link building,one of the most important aspects of SEO is classified into 3 basic types.
one way,two way or recirpocal link exchange,three way.

One way Link Building:
Building One way link is sometimes difficult/easy depending on situations.It is difficult in certain cases,in that, the other website owners need to link back to you automatically.This can happen automatically only if the site your handling contains unique and interesting content.In other cases,one way linking to you site becomes easy when we place comments in other blogs(without spamming),which are dofollow.

Two way Link Building/Reciprocal Link:
In this type of link exchange,a give and take policy happens.You site link is placed in another domain.
Their domain name will be placed in your website.

Three way Link Building:
This is one of the little known techniques.Assume you have a website "A" for which you need a good
backlink/inbound link.Assume you have another website "B".Utilising these 2 sites and contacting another website "C" you can perform 3 way link exchange.During this link exchange,the website "C" places your link "A" on their website.And instead of placing the website "C" in site "A",you place the link in your other site "B".
Thus you are obtaining a backlink to "A".

Check the posting here v7n.com/forums/seo-forum/131174-need-link-building-advice.html