How do I negotiate a job offer/salary?

I’m just wondering how to negotiate a salary in an appropriate manner in case I need to.

I (hopefully) will be offered a job from a specific company soon, and as far as I know their salary range and my expectations are on the same page. But just in case it isn’t, I’m just wondering how to bring it up. For example if the salary they offer is on the lower end of the range, or if I want relocation assistance and they don’t already offer it. Would I be talking to the higher ups? HR? I want to do this in the most professional manner possible but I’ve never done this before so any advice would be appreciated. Thanks in advance

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