Keep your composure, as Mikey always says. We have all been guilty of it: the timer beeps, panic sets in, and we take off like a bat out of hell. In this case, composure means not coming out too hot. Nobody trying to have a successful Murph experience is planning to PR their first mile.
Hydrate the day before. Beer does not count; trust me, I have already tried this for you.
Keep a measured pace throughout. This might mean breaking up the push-ups early if they are tough for you, or remembering to breathe through your nose as long as possible. See tip #1 and try not to blow out your first five rounds then become epically slower for the rest of the workout.
Set a realistic goal: If you have never completed Murph in full, a smart goal may not be to do the WOD straight through with a weighted vest. Set a goal based on last year (or any previous attempts at Cindy in class) that is small, attainable, and satisfying. Maybe your goal will be to not break up any sets of pull ups or squats, or to shave a minute off each mile.
Maintain virtuosity even when you're tired. Reps with shitty form technically count, but all you're doing is reinforcing bad movement patterns dozens--or in this case--potentially hundreds of times. Watch Kelly Starrett talk about how bad movements patterns always lead to injury. Slow down if you have to, but don't compromise good form, even in your last few rounds.
Mind over matter. It is no surprise that at some point in this workout you might want to quit. It’s kind of the point. Anticipate that moment ahead of time, and decide what you will tell yourself in these moments where you need to dig for grit. You may remember that this workout commemorates someone who withstood much greater amounts of pain than any of us will in this WOD. You may think about a person in your own life who is suffering in another way, and dedicate this workout and all its pain to them. Have a plan for the moment when you want to quit.
Keep perspective. Remember, it's just a workout. Someone died for this day to exist. So whatever happens during Murph, in the realm of life, it is small in comparison.