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You can set up folders by genre, for example Deep house, House, Funk etc.
You can name folders in whatever way suits you – when I started I named them House Major (for up beat tracks), House Minor (for downbeat tracks) and so on.
On Serato there is an option for ‘Smart Crates’ which allows you to file by BPM, Key, Comment and may other options.
When starting out its probably best to go by genre though, you will figure out what way suits you from there.