Everyone understands the concpet but no one can follow it perfectly
1.the killers ability shouldn't make him stronger but harder to counter by survivors
2.every killer has to have something to counter pallet looping in a way
3.don't stray too far from the killers classic stats

Perks
1.same as rule number one with killers
2.the perk is clear and not too complicated for survivors (hex: example, for every survivor being chased for 20 seconds the killers field of view increases) survivors don't even know that he has the perk
3.perks aren't add-ons they can't help a killers abilty

choosing those categories for your killer is extremly important (with examples for each category)

Hunting killers: Hill-billy, nurse, huntress, doc, hag, wraith?
Brutality: Trapper, cannibal, hill-billy, shape?
Ability: Nightmare, wraith, shape, nurse

Hunting- killers about closing distances fast and getting hits faster than other killers
Brutality-killers about finishing the surviovrs off and hooking them as fast as you can
Ability-killers that use their abilty to skip over hunting and use brutalty in a diffrent way

Global presence: Hill-billy, nurse, trapper, hag
Speed: Wraith, huntress, cannibal, doc,
In need of a buff: Nightmare
Other: Shape

Global presence: speaks for it self
Speed: killers who get stuff done fast so they could go and inflict their presence
Freddy is weak and useless right now
Shape is mostly about speed but since you will stalk instead of chasing he will run around survivors most of the match inflicting his presence so he's both