Links which are related to niche can be blogs,directories,forums etc are the best source of quality links>To make link count on your site just dont drop the link make a real effort by suggestion,by praising etc to let Blog Owners or Moderators feel that they have shared a good,helpful resource
Backlink means Link exchanges. It can be good, and can be bad. There are a number of services out there that will connect you with other similar websites or totally random sites to exchange links with. Some search engines penalize these sites, often referred to as "link farms." There is a fine-line drawn between link farms and link exchanges.
Backlink to avoid
Don't submit to sites that aren't relevant to the focus of your site.
Avoid pages with links inside of frames (this will steal your traffic).
Don't submit to blog networks and limit blog rolls
Don't submit to article networks (they post your article to multiple sites).
Don't let anyone link to you from every page of their website (sitewide links unless they are nofollowed).
Free for All Links - they allow anyone to post a link unreviewed which results in unrelated and spammy links (banned by search engines and may also affect your site if you link to it).
Link farms - 100 or more unrelated links on a page (banned by search engines and also your site if you link to it).
Bad Neighborhoods - Poooorrrrnnnooo or gammmmbling or drug sites (banned by search engines and also your site if you link to it)
"I'll link to your website if you link to my other website over there" is called a Triangular Linking Scheme(can cause your website to be penalized or banned).
The site has a network of mirror sites with exact same web links (these sites may be banned and your link on their site will produce no benefit).
Avoid submitting to directories that don't review submissions and let anyone in.
Avoid submitting to directories that have several Google ads disguised to look like their own content above the other links as they are likely to be penalized.
The link page or directory is not linked from their home page or site map (search engines won't find your link).
If the website is supposedly a directory but you have to search to find anything your site won't be found by Search engines.
If the backlinks on the page have a rel="nofollow" tag on them the search engines won't give you credit for the PR (page rank). Some directories are doing this to protect the PR of their page (it won't provide PR but may bring you traffic). However, even though most local sites put "no followed" on the link, it can still help your ranking a little bit (called a citation) so don't ignore those. The website takes forever to load (too many ad banners, etc.) and search engines won't wait which means they won't index your link on their page if it's at the bottom of the page.
The website is poorly designed and has broken code, etc.
Avoid sites that insist on a link trade as the only option because search engines may devalue all their links when all their links are traded.
Don't submit to sites that have no contact page in case you want to remove the link later.