Get the opinion of the person who rejected your post. What was the missing link? What factors did you ignore? Don’t be afraid if your post is criticised as it gives an opportunity for you to improve. Knowing that you lacked something, you will probably focus more and try to be successful in future efforts.
More often, it is not about the content of your post but the structure of your writing or incompatibility with the blog's genre. Most expert bloggers may want a rough draft mailed to them first before they decide to post it. Therefore it is essential to figure out the missing links first before drawing any conclusions. It is better to know the reasons of the rejection rather being given no or little feedback.
Act on the advice
Taking advice is one thing and acting on it another. If you want blog owners to accept your guest post, it is important to play by their rules. Don’t just dwell on your own philosophy and make sure you align your post with the needs of a particular blog. Read the necessary or specific requirements blog owners want for guest posts and try to meet those.
Re-submit your rejected post by incorporating the style, technique and intent a blog owner has pointed out. Reading some of the related posts can help you improve.
Find another blog
If you feel that you are having trouble matching their expectations, try another blog. The rejection may be simply due to the fact that your content or style does not align with their methods. However, it does not decrease the value of your post so it is important to pursue other avenues. The post may be too political or gender biased for a particular site and may be accepted by another blog.
Ultimately it will pay off. Rather than getting discouraged, it is essential for you to keep on trying even if your guest post is rejected many times.