Naturally link development is the best, why? because google likes it. Don't use link trading sites there a waste of time Buying links that are do-follow violate google tos and can penalize you.
^ Yeah right! Like engaging in forum submission or any off page optimization just be sure you includes your links! And observed if where you usually gain your quality links then stick with it!
maybe you can write comment in other Blogs and put your link in blog comment and you will get natural link from visitor.
Natural link is by far the best, but could take some time. Otherwise, I find it that building backlinks by way of article marketing and press releases is one of the better if not the best way to do so.