It really depends on which social network you’re posting on. On a Facebook Page you should post 1-2 times a day.
On Facebook Groups you do not want to post too often as you want members to see the notification and be interested in what you have to say. There is a fine line on posting too much and not posting enough.
Posting to a Facebook Group 3-7 times a week, depending on your audience engagement rates, is a good idea. You can post to Twitter and Pinterest much more frequently.