Guest posting is quite an honor. Someone is trusting you to connect with their readership. They trust that what you have to say is valuable and interesting.
It's an excellent marketing benefit, but takes additional time out of your day to research the blog, write the post to fit the unique ambience, and go back to respond to comments. Sure, you can just send over a guest post, but what if it doesn't fit the blog theme?
Take the time to read several blog posts where you will be "visiting." Become familiar with the blog author's followers.
When guest posting, I've always felt more blessed than those I'm supposed to be blessing. I'll admit I'm always surprised that what I wrote helped someone else. Not that I don't expect to help people--I do. But writing a guest blog is a little tougher because on any given day, no one really knows if people will come to read and comment.
Rest in the writing. No one can guarantee writing a guest post will be the most amazing thing ever. But when we write, the story is in God writing through us.
What is it God is trying to teach?
Is God teaching it to others or to us?
What's the message between the lines?
May God use your writing as a guest poster to bless and encourage others while blessing and encouraging you.