Another tip besides extensive knowledge: Be passionate about your content. If you find yourself sighing throughout the writing process or taking too many breaks that make you happier than the topic, that could be a sign it isn't the topic for you. Not saying that you hate being an electrical engineer or find computers tiring. But it's just one of the things a lot of people forget to remind themselves once they find out they can earn money writing what they know.
I made a blog a year ago and am receiving an alright amount of traffic. I have meh followers, but it's good considering I don't promote my work, like at all. I also don't post often, so that amount is even better. Know that you need to put a lot of your time, effort, and money into blogging. Money is optional, but it helps show your potential readers that you're legit and serious about the stuff you write.
If you're going to blog, don't forget to use keywords! Keywords help so much with receiving traffic/fans. I have a feeling that could be one of the very few reasons why my fanbase exists in the first place. Besides the super-duper content, of course.
Good luck with blogging!