Guest posts are very effective forms of do-follow link building and the guest posts that I produce are of a very high quality. So I write a high quality blog post around the keywords that you are trying to rank for and then post that on a relevant blog which has good metrics such as Domain Authority and Trustflow.
I make sure that these posts look very natural so they are not labelled as a guest post and I always include one other relevant but non-competing link in the post so that it all looks very natural. And the content is of a very high quality and I use natural anchor text (so usually some keywords but also other words so that there is lots of variety and very unlikely that this specific anchor text will have ever been used before), these are strong links so it is best to include some keywords to get the most out of that link strength.
I would suggest that you have some links to your web site in place before ordering this, I can build diversity links if needed so see those in my profile as you should always have a diverse back link profile before building strong links like these guest posts.