Keywords are not case sensitive and it doesn't matter whether the keywords are used in uppercase or lower case letters.
But do your best to have good grammar on your blog posts and titles to show professionalism and gain readers and blog traffic.
If you want to earn a living on your blog you should always proofread your blog posts before publishing.
After writing the content, then go over the blog post to ensure no spelling errors and if there's spelling errors make sure you correct them before publishing the article.