Hey Julzwriter, since you've been here on the forum longer than me then I assume you know that your content needs to be really good in order to be approved for a guest post.
If you believe your content is not fluff then you might want to change your approach. Start by building a relationship with the bloggers. The best way is to start on their comment section, to build trust and establish your authority in your niche then add some valuable comments on top blogs in your niche.
But this strategy works best with blogs that are frequently updated and make sure that you do this while the article is still fresh and getting social media activity. What you want to do is to read their new article then in the comment section add anything that they missed.
You don't want to overdo this, just make sure you do it when you're 100% sure that you can add value to the post. To get even more out of this strategy you can even answer questions in the comment sections if you've got some value to add. Always follow up on every comment you create, maybe keep a text file with all links that you commented on and check them once in a while.
That's the easiest way to build your rep/authority and be able to approach the bloggers more easily. All you can do from here is to let them know that you've been following their blog for a while and you love their readers. Maybe even share a comment where you helped someone but as a story don't post the blog post URL in your message.
When they respond you can then build the relationship further and later pitch your guest post. This is a strategy I use on people who don't promote that they accept guest posts so it should definitely work on bloggers who already accept guest posts.
Doing this will help you stand out from other guest bloggers and you'll be like a friend to these bloggers because you communicate with them and you help their readers. But this is time consuming and requires patients.
I am in complete agreement of what Nytshade said. I put in another vote for what he said.
It's worked well for me, it's gotten people coming to me, asking me to do guest posts. And frankly I'd rather be asked, than to bug people. It can also get you included in round up types posts. Or other blogger friends putting links to your content in their posts. Happens all the time if you take part. Or, it can build you a group of people that share your content social every time you put out a new post.
And yes, as Nytshade already said, the relationship is SO important. You need to actually interact with others, not just the blog owner and their content, but also other commenters as well. So many people don't seem to get how to build relationships online, or worst they don't care, either way it get's them no where fast.
It comes down to thanking people or acknowledging them when they've helped. Don't leave the same comment as some one else without acknowledging the other person, or adding to it. It's about giving first to get later (that's is a biggie). Social sharing other people's content so they will eventually start sharing your contents.
Be a part of the community, because so many blogs are just that. Least the ones worth looking into.
I would say that you really gotta know what you're talking about. Read a lot about the subject that you are blogging about. Reddit and Quora are great places to get information from before it gets popular or saturated.