Any advice on fasting?

I’m planning on starting a juice fast in a weeks time, as from what I’ve seen fasting seems to be a common denominator in a lot of people’s progress and healing.

Does anyone have any advice on doing this? Is a juice fast worth it, or just water fast?

Some people say water fasting for quite a while (even past two weeks) is necessary but that seems a bit out of the question when I consider having to go to work and actually functioning through the week.