Read.
That's literally it and it is scientifically proven to improve vocabulary and has plenty of other benefits, too.
Books are better than short articles or reading on screen, but reading anything that keeps your interest is better than nothing. Look up words you don't know. Falling down wikipedia rabbitholes can be fun, too.
Since you know how to engineer toothpaste squeezers, you are probably a STEM-person. I'm a humanities guy and there is kind of a meme to see phalluses in everything when it comes to cultural or artistic analysis.