Sitting around waiting for good ideas almost never leads to good ideas.
If you only write when you have a novel idea that you are inspired to write about, you will end up not blogging very often at all. That is why you can’t act on the condition of having a good idea.
If you commit to writing whether you have a good idea or not you create an environment for generating ideas. You pay closer attention to your thoughts and observations, and you notice and track ideas that may have passed you by. You have a personal incentive for coming up with ideas (because you don’t want your blog post to suck) and as a result, you have way more ideas.
A lot of those ideas won’t lead to anything but some will be great ideas that you would never have thought about if you didn’t have a need for them.