One of the things that derailed early attempts at fasting was a kind of wishy washyness to start and end times. When someone put me onto the 36 hour fast, this entirely resolved.
The 36 hour fast is simple: you eat dinner, then you fast the entire next day, breaking the fast when you wake up with breakfast 36 hours later. There's not a lot of ambiguity in this, you just skip an entire days worth of eating.
From there, you can extend out your fast, or pull it back as circumstances dictate.
