What proofreaders do
Proofreaders make sure the translator's script is free of grammatical and spelling errors. They are also responsible for making the dialogue flow without destroying the original meaning of the translation. They can also be responsible for crafting dialect speech for certain characters.
What you will need
A near flawless grasp of English grammar, usage and spelling.
Some knowledge of kana is helpful.
Programs to fix the translation scripts and track changes or put changes on separate lines e.g. Word, Scanlationshop, Notepad 2.
Notepad 2 (Great improvement to notepad)ScanlationShop
Dialect Generator (LOL)