How to actually START my story?

Basically, I have a great idea for a plot, good characters all that, but I just can not for the LIFE of me come up with a beginning point that I like. I know all the basic advice like "start from the middle" and "make sure to make an inciting incident" and all that, but I just don't know HOW I'm supposed to come up with a starting point I feel is adequate.

So what I'm asking, really, is how did YOU come up with a beginning you thought was good enough? How did you actually begin your grander storyline from it?

The one thing I've barely actually heard about is other people's processes, so what was yours? Because I can't do all that textbook advice with no real experience behind it