なるべく is a single, fixed adverb that means 'as much as possible' or 'if at all possible.' It's often used when giving advice, making requests, or stating intentions to do something to the greatest degree possible. For example, in a sentence like 'なるべく早く来てください' it means 'Please come as early as possible.' It carries a nuance of trying one's best or minimizing inconvenience.

You'll hear it in both spoken and written Japanese, but it's more common in polite requests and formal statements. It can modify verbs, adjectives, and even other adverbs. When used with a verb, it often appears in the form 'なるべく + verb (dictionary form or te-form depending on the sentence).' For example, 'なるべく避ける' (avoid as much as possible) or 'なるべくして' is not used; stick to the basic adverbial use.

A similar expression is 'できるだけ' which also means 'as much as possible,' but なるべく has a slightly more subjective or intentional nuance, like a personal decision to try hard, while できるだけ is more neutral and factual. In everyday conversation, できるだけ is more common, but なるべく is still natural and polite.