When you fast

Probably the biggest key to remember is that fasting should not be a religious practice to try and convince God to do something.

Fasting does not change God, it changes you.

Hunger is probably the strongest urge of the flesh. When we fast, we are telling the flesh that we choose to follow the spirit and not the flesh.

What fasting does is help you discipline and get the flesh out of the way. Once the flesh is out of the way you are more sensitive to the Spirit and hearing from God. The flesh is the source of a lot of doubt and unbelief, so your prayers can be mixed with unhindered faith when your flesh is under subjection.

I don't know how many times I've been busy at work and gone all day without breakfast and lunch without feeling or realizing it. However, the moment I decide to fast, immediately the flesh starts pinging and wanting immediate attention and gratification (hunger pangs, headaches, wooziness -- and it's only been 5 mins!)

In the broadest sense, you could probably consider a fast anytime you are denying the flesh one of its appetites. Strictest sense would be no food or water. Best to start small and work up over time, maturity, and leading of the Holy Spirit. Keep in mind, you are out to discipline the flesh, not kill your body.

Jesus said that when we fast, we should go about normally with our daily business as if we are not fasting. It's not anyone's business to know. If they ask, don't have to be spooky about it, just say you have other plans for lunch.

Use any hunger pangs as reminders to pray or ponder a scripture verse. Every time the flesh rises up, remind it that you don't live by bread alone, but by the Word of God and that your meat is to do the will of the Father.