Work your way up to longer dry fasts gradually. I increased by 1 day at a time, up to 7 days. Nowadays I typically stay in the range of ~3 days and normally don’t go past 5 days, for me it can be very demanding on the body, especially in combination with work, hot weather, an active lifestyle, workouts etc.
Make sure to hydrate thoroughly for a few days, especially when going on long dry fasts. I enjoy lots of fruit (mainly watermelon) and coconut water beforehand, works great for me.
All the best on your fasting journey!