In addition to these good answers you are receiving from these other experts, I would like to add another consideration, and that is you would be wise to be careful in your selection of bloggers to approach. It is not about quantity but quality. You should research who are the bloggers who are key influencers in the subject(s) most related to your product or service. Then review their sites, policies, and media kits if they have one. Some bloggers accept guest posts, many do not, almost all will charge a fee for product reviews and sponsored posts. Do not contact any one blogger until you determine that he or she seems to be a good fit for your purposes. Then you will see if that blogger is interested in working with you. The generic approach is a poor strategy - bloggers are individuals and no two are exactly alike.