1) Make Sure you have relevant anchor text else that link is waste
2) Avoid getting image links, if text links are possible. Text links should be priority
3) To get maximum link juice make sure you get links from the pages that have very few links.
4) Avoid getting links from pages that have not been cached since last month. Those pages may be dead and as a result your link will be dead
5) Avoid Getting links from irrelevant site.
6) Avoid Selling or Buying Links explicitly. If you have to do it, do it through creditable link brokers.
7) If you have have image link, make sure you ALT text.
8) Avoid getting links from spammy websites. To check whether website is spammy or not just visit the website and you will know