How Links To your Website Improves Your Ranking
One of the aspects that centrainly Google takes into considuration is how many sites are linking to your url.
But they also take into account where these links are coming from!
A link to your site from an other site that has a High PageRank is more likely to boost your ranking than one from a LinkExchange directory.
The last one might even bring your ranking down, becouse in some cases your are in so called "Bad Social Neighboorhood"
So it is very important that you get the right links from the right sites!
Also the description of your links are important:
A link to you website that is like "Click Here" is less of an improvement than a one like "Network Documentation and Network Management Information"
Although Both link to the same website, you will see that the last one is pick-up bij search engines as more relevant to your keywords.
So If you are going to build you network of link partners, look for sites in the same area as you are and preferrebly handle the same topic.
But try to get links containing your keywords!.