I think Comicalflop who made the TAS is the only one who looked much into frame data. Some of it is mentioned here: http://tasvideos.org/GameResources/N64/MischiefMakers.html For other stuff that isn't on there you'd probably have to test it yourself.

Optimizing your movement is the most important part for sure and the best way to do it is probably playing levels (especially platform heavy ones) over and over. However i guess you could also do it by just grinding runs if you prefer that. The more you play the game the better your movement should get. Most of the techniques like slide jumps, fast boost grabs, dashes to gain height, etc. just become natural after a while. Other than that you should practice the most time saving strats like boss quick kills and missile surf (don't bother with super hard stuff like 1-5 TAS route or frame perfect worm kill until you are really good though). I also think it's really helpfull to watch a bunch of runs from different people, discuss strats and experiment yourself. MM is an very open speedgame and if you look at some runners you'll find that pretty much everybody uses different strats and optimizations. This should help you finding the route that works best for you for each level and give you a base to improve on as you get better at the game.

Thats pretty much my approach on how to get good at this game in general. If you are having trouble with specific strats or basic techniques (boost grabbing, clipping) Jack's FAQ from the post above and the TAS notes linked in them might help you. If not you'd have to describe what exactly your problems are.

Hope this helps!