One of the things learned and I read in my book "A twist of the Wrist" by Keith Code
You will practice noticing with visual recognition what speed you are going, and know what gear to be in to accomodate getting the bike in its best power band range of Rpm's.
I use sound to shift too, hear the sound of pissed off bee's get louder as you open up the throttle, even with my music blastin on my helmet speakers lol
Highly recommend the book, its like a bible for riders.