1 per day: If you have just started blogging, then writing consistently might take time. So set a target to have 1 post per day that is well researched.
Grammar - Depending on the language you use, blogging just makes it imperative that you are reasonably good with your grammar skills and proficiency if not a master. Remember your audience is a mix of both; the ones who are experts and the ones who are not.
Originality - Focus more on the originality of content and on a consistent basis. It is a habit you will need to cultivate.