I would try to figure out those difficult words from context clues first and if that doesn’t work look it up. It will help build your vocabulary, which is also how you would build vocabulary in your native language. But it is okay to skip it occasionally if it doesn’t effect your understanding of the sentence/paragraph.

I suggest that you ignore the unfamiliar words and just keep reading. Only look up a word if it stops you from understanding an important part of the story. If you spend too much time looking up words, you might get bored and lose motivation. You will understand lots of words just from looking at the context and the words around it.

If you are at an advanced level and you want to get better, it seems to me you are going to have to look up words whose meaning you do not know. The problem is that you can spend a lot of time looking up words that you may never see again. You want to try to focus on the words that are more common that you don't know. So you might adopt a strategy of looking up words that you don't know that seem to be familiar to you, because you have seen them before. It is tedious looking up words all the time, but you won't improve unless you learn new words or at least see words you know in new contexts. Anyway, this has been my experience in trying to learn French.