When should you blog? Well, the answer to that is as personal as when should you write? What's your best writing time? When does your life allow for writing space?
Your blogging is just a part of that. It's "real" writing, and you need to consciously schedule time for it. One day a week? Perhaps you'll opt to write three related weekly posts on Monday. Or daily? Maybe you'll post something on your blog after dinner, each and every day.
The important thing is that you make time for it and do it with regularity. This is part of what will make your blog interesting to readers, and easier for you to accomplish. All the habit tricks you use for other writing apply to your blogging as well. Trust me, it's easier with a plan and discipline.
It's all part of your commitment to succeeding as a writer. Read Teagan Oliver's comments about commitment here.