What if you don't know a word?
First, decide: is the word important? Do I need to know it to understand the text?
Strategy 1: decide what the word means by looking at the context. Is it a verb or a noun? Is it positive or negative? Does it contain parts of words you know?
Strategy 2: if you are allowed to have a dictionary, look up the word. Watch out, this takes quite a lot of time!