I'm currently reading Schismatrix. I'm loving it, but I also realize I take a long time to read it because of my currently rather limited english vocabulary. When I don't know a word, it usually doesn't prevent me from understanding the whole sentence. I lose nuances, but I still get the meaning. It's roughly the same when reading a book. It's not because I don't get a word or two in an sentence that I won't enjoy the whole plot. But these words bring color to the scene. They add details. They can be used to fuel my brain with extra data point to make the story even more vivid and immersive.
So I've decided to stop at each word I don't understand, and look for a definition. No matter how unimportant that word is for the plot. If it's chosen by the author in that situation, it's probably for a reason. And with that increased vocabulary, I'm hoping it will make my readings even more interesting.