I would start with, what is considered, Tier 1, High Authority backlinks.
But don't just create random links. You need a comprehensive strategy. If you're going for specific keywords, then i would check the backlinks of your competitors using a tool like AHref and target the sites that you come up with.
Also draw up a list of blogs and websites offering guest posting services in your niche. Again, aim for high authority domains. Email the sites offering a guest post, write a contextually relevant article, include your link, and hope it gets published. Alternatively contact a writer, publisher who sells backlinks on such sites to do it for you.
Another popular strategy I like to use involves creating "link bait" articles. Publish viral content on a blog on your site and send to as many media sties as possible. Hope that they link to your article in one of their articles and reap the link juice.
After that, you can consdier social bookmarrking and Web 2.0 properties to your Tier 1 links