Exact steps on adding a ROM? Galaxy s3

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http://androidforums.com – So I want to put the MIUI V4 ROM on my Galaxy S3. It's completely stock. The question is what do I do first? I'm on stock recovery. Is it Root, add a custom recovery, then flash the ROM? Or does a custom recovery automatically root it? I've looked at a couple of guides, but they're all in pieces. I just want the exact instructions for my Metro PCS Galaxy S3 so I could minimize potential error. Thanks in advance!!:D (General)