What kind of keywords should we use while doing blog, exact keywords or long tail keywords?

Long Tail Keywords because Long-tail keywords tend to stand out more, and readers might catch on if you use it every other paragraph. Try to use it in the title, at least one header, the first paragraph, and occasionally throughout the text.
Make sure you're using the keyword naturally, rather than stuffing it into sentences where it doesn't belong.

Long Tail Keyword

Make sure you're using the keyword naturally, rather than stuffing it into sentences where it doesn't belong.