Active reading means entering into a conversation with a text. Ask what the writer wants to say, why a particular word matters, and what other interpretations might be possible.
You do not have to look up every unfamiliar word immediately. First notice how it works in the sentence. Then record the expressions that seem most useful or memorable.
Try this: read a paragraph twice. The first time, focus on the main idea. The second time, choose three expressions and use each one in a new sentence.