trying water fasting for the first time

what are some dos and donts? i know water is allowed, what about coffee? i especially like consuming turkish coffee which is like 7 kcal per cup apparently. what about instant black coffee?also anything i should know beforehand? im wondering how to keep energy levels high and brain working efficiently after like 10 hours because when i get hungry my body becomes weaker and brain starts to become dumbalso for how long should i do it? i heard online that 3 days is the default but idk? via /r/intermittentfasting https://ift.tt/Ww4kbLM https://ift.tt/ropwRtL