Are you looking to guest blog on other blogs related to your niche?
I personally wouldn't guest blog on just anyone's blog. You want to leverage your time effectively and reach out to those that have similar audiences as you.
Guest blogging to just blog on someones site for me is not a good strategy. I look for bloggers who have a strong authority in their niche and are active in their social media communities.
Leveraging these kinds of relationships will help me to grow my blog traffic much quicker than posting to a blog that doesn't have influence, authority or a growing community.