How do you avoid having grammar mistakes in your writing before posting it to your blog?

The best thing is to use proof-reading and spell-checker software. There are plenty of them online. Grammarly is one of the best out there.

Use proofreader software, the one embedded into Microsoft office is efficient enough.

Use spell-checker and do some proof-reading

trying to make a thorough proofreading for any document.

Grammar is one of the essential thing that you never want to avoid. Grammarly is the best option for the grammar check. Second point is that, its all about the command on language. The more you have command the less you made mistake.  

Well, that's a good question because, in my case when I feel severe fatigue and headaches, I turn dyslexia and that can happen anytime.

The best thing to do is proof-read each paragraph as it is done rather than skimming the whole article once or twice.

P.S In my case, I find the online platform/plugin/chrome extension Grammerly very useful.