Any brand guidelines. Tell me your target audience, your brand's tone, your brand's message.
Brief me on your blog's topic. Tell me your ideas, your dos and don'ts and we can make magic together.
SEO focused Keywords. What keywords do you want to rank for? If you have absolutely no clue, don't worry. I can do a little research for related semantic, low hanging fruit keywords that will add "flavor" to your content.
Marketing / Blog goals. What are your goals for this particular blog post? Is it just to inform? Or are we converting? Are we directing prospect traffic to a particular page on your website?
Speaking of converting, what's your CTA at the end of your blog post? Are we directing traffic to your contact list, email subscription, service or product page?