Preparing for a start

Can i have some advice on what to do before a start on the weekend, such as saturday at 4pm?

You can always do some stretching and long toss.

Important: when you are warming up prior to that start, you need to throw all of your pitches to see how they are working. If you find that one of them is misbehaving, stick it back on the shelf and concentrate on the stuff that is working for you. There are few things as bad as going out to the mound to start a game and then finding that, say, your curve ball hangs, or your slider is flat, or your knuckleball refuses to knuckle, and the other team tees off on those pitches. And it’s better if you know about this beforehand. 8)