One of the best and safest technique I consider is guest posting. It does not violate Google TOS of buying links. At the same time, it is easier to achieve if you will offer good content to webmasters. The thing is, some sites collect fees to offset website management cost and cover other expenses. If that is the case, then sponsored post won't be a bad idea.
The safest way to get links is the lack of gain. I'm talking about natural links that come themselves. If you manually add something then keep in mind that you need time to increase the number of links, stick to that principle and will be fine.
Backlinks from social media sites are the safest, and the most powerful. If you post a link to your site on your site's Facebook fan page, then you have one backlink. If one of the users share that on their wall, then that is another backlink. Search engines look favorably on a page that is shared and passed on through social media sites. Hope that helps. Have a good day!
A few link methods: Submit your site to quality relevant directories. Some of these will cost which will help deter spammers. Joining local business groups can also sometimes get you quality links. Consider the Chamber of Commerce or the Better Business Bureau as well. Use Twitter and Facebook to build links. Repair broken links that you already own. Guest posting and blog commenting are popular ways to build links. Forums, press releases, and videos offer more link options.
Create quality Web 2.0 and generate some traffic and backlinks on them. because they possess high Domain authority. if you place your site link their, Google consider it genuine link.
Anything that looks natural in the eyes of Google is safe after these various Penguin refreshes. For me following comes under safe linking strategies: - Guest Posting - Directory Submission - Web 2.0 creation with ulta high quality contnet. All others, like blog comments, forum posting, profile links, social bookmarking come under the radar of spamming for me. Everyone who is looking for a long term benifits for its online business should refrain from implementing any spammy link building strategies, otherwise sooner or later Google will catch you and you will have to face the penalty which can be hazardous for your online business. For me, in SEO, slow and steady wins the race, build quality links, even if you are building only 5 a week, just concentrate on quality and not on "the number of backlinks" For a more detailed idea of which strategies you should go for and which you should avoid, give this article a read from SEOMoz - http://www.seomoz.org/ugc/5-penguinfriendly-link-building-tips
I agree with guest posting and web 2.0 comment backlinks, I think the most important thing is just to get a variety of backlinks, don't stick to one type of backlink and just build them slowly and naturally
Post articles on relevant sites Get links from relevant authoritative sites Guest blogging on relevant blogs
Guest blogging is too powerful these days, you should concentrate on this method too, apart from this, I would say that you can create content regularly it would also help in ranking higher if your site has quality content created at regular basis, there is no doubt to it.