The only way to make sure to write consistently is to schedule time for it every day. It will happen that you find a topic that you want to write about right away and kick the ground running. Most of the times you won't and you will be staring at a blank page.
The best way I found to write consistently is to have a pool of ideas always ready. If I sit down to write and nothing comes out I just pick one idea randomly from my list.
Another way would be to always pick an idea from the list before you start writing - I usually pick it the day before - and stick it up.
I'm against setting a minimum word count for blog posts. If you were writing something longer - let's say a novel - and you wanted to make meaningful progress on it than that's the only case when you should. When I do that I usually start gradually, first 500 words, then 1k, then 2k.
The morning is when you have the most energy, and that's when you should write. When I did commute by train I spent that idle time to write. Now that I use a car I don't, so I write in the evenings and instead write ideas down in the morning. Being a programmer I'm more of a night owl, than an early riser as many writers are.
1. Write every idea down
2. Pick the best ones
3. Allot 30 minutes to write every day - you can pick how many, 30 feels the right amount of time without it being a huge commitment
4. Show up and do the work
You're always going to be busy. If you really care about writing, you need to find the time, somehow, somewhere.