I like what most have said and here are some favorites for me...
"Slow is smooth and smooth is fast. "
"organization/consistency - set things up exactly the same every time "
"Repeatedly visualize every step of your transitions. "
The others are great too but when I set up transition I make sure it is very simple. Almost too simple because every time I finish setting up I think I am forgetting something. For T1 I have my helmet and glasses. For T2 I have shoes, socks, race belt and maybe visor. This makes it easy for me to have ZERO clutter around my spot so I don't forget anything. Also when taking off your wetsuit toss it to the back of your rack area, while keeping it in YOUR spot, so that it isn't on anything you need in T2.
Running into T1 pull your wetsuit down to below your hips so that it's easier to get off and if you can put helmet/glasses on while taking suit off. Coming into T2 start thinking about how you're putting this on, bike seat first? Handlebars first? (obviously this should be figured out before hand but mentally going through it right before is good too) Once bike is racked take helmet off, put on socks and shoes then grab race belt and put that on while running.
I really do think the biggest thing is keeping things simple in transition. The more clutter around your spot and the most stuff to put on the bigger chance you have to forget something.
But you are one lucky guy to be able to take triathlon training as a class!
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