The best days of the week to post are Mondays, Tuesdays and Wednesdays.
I would never post more than once a week about the same topic. Also don’t be afraid to create all your posts for a particular campaign. Just let us know when you want them posted and they can be scheduled to the minute.
Other than that there are no hard and fast rules. Try to write topical posts that pick up on current events in the media. Has a recent newspaper or television programme picked up on the subject you’re covering?, Try to piggy bank off current stories and relate these stories to your own. This is the best type of post as journalists are always looking out for other stories that complement there own.