Hi,
As with most things in SEO, the answer depends. It depends on how many UNIQUE topics you can generate and how long you're willing to spread those out over. Unique being the keyword there.Don't just go out and write X amount of posts per week because someone recommended it or your read it somewhere - that's going to lead to crap or topically-identical content just so you can fulfill a quota.
Make a list of topics for posts, as many as you can that are unique and worth having their own URL. If you start to get too many posts that are basically the same, Google won't rank either as they'll view it as a spam tactic. Once you have that list, prioritize it in terms of average search volume for the keywords you've associated with each post. Then start with 1 or 2 posts per week. If you see good results from that, consider ramping it up. If you're not seeing good results, step back and shift your strategy.
As Andy said, there's no right answer to this question, but there are smart ways to plan your approach. Just remember to keep your posts unique (yes, I am saying that a lot, because it's important!), the best way to rank is to show Google something new that they haven't seen before.
Happy blogging!