I have problems with that myself. By wanting back links, I assume that you want them to help your site ranking as google gives more credence to a site when they see other sites linking back.
The best way is to contact other web masters and ask them to link to you. The problem with that is they will want you to link to them. Search engines penalize that. They want links that are not reciprocal.
The best way is to ask to write guest blogs on other’s sites. What you want to watch out for is if they use no-follow-links (all social media sites do this) which render your back-link useless.
I will happily let you guest blog on my site but It is mainly a technology blog. I would want unique content but you can place a reasonable number of back links to your site just as long as the content is not spammy.