越 (yuè) is used in pairs. 越 A 越 B means "the more A, the more B": as one thing grows, so does the other. 越来越 means "more and more", for something that keeps changing over time.
Subject + 越 + verb + 越 + adjective.
With one subject, the first 越 goes before the verb and the second before the result. 雨越下越大 says that the longer it rains, the heavier it gets. 越 always comes after the subject, never before it.
Subject 1 + 越 + A, subject 2 + 越 + B.
Each part can have its own subject. Put each 越 after its subject.
Subject + 越来越 + adjective (+ 了).
越来越 says that something keeps changing as time goes by. It goes before an adjective, or before verbs of feeling such as 喜欢. The sentence often ends with 了, because it describes a change.
越 already means "more", so don't add 很, 非常 or 太 after it. 天气越来越很冷 is wrong; say 天气越来越冷了. The other common mistake is to forget the second 越: 他越走慢 should be 他越走越慢.
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