biggest things:
learn to hit every single L cancel. Practice against the air and against people, short hops with and without fastfalls, full hop aerial land on platform L cancel (this is crucial for continuing combos). what Makr said is a great way to practice, try it on air and on enemies. For practicing this solo, you have two good options:
1) if you have 2 controllers, plug one of them in while the stick is all the way up. put the damage ratio to .5 and handicap such that your handicap is 1 and his is 9. select bowser for him. you should be able to dair shine him up to 400 or so.
2) if you don't, do all of the above except with a level 1 bowser who isn't crouch cancelling.
wavedash consistently. especially out of shine. take a lvl 1-3 fox or falco to FD and dair, shine, WD forward, dair, shine him for a while. this combo only works up to about 40% on humans, but will work longer on CPUs. WD out of shield is useful too.
learn to laser at all the relevant heights: SHL at the top of your jump, middle, and very close to the ground (close enough to hit a crouching kirby or a fox who has missed a tech, for example). Learn IDJL (instant double jump lasering). jump, double jump immediately (just press x twice really fast) and then laser twice. The first laser will come out near the top of your jump, and the second one will come out at different heights depending on when you fast fall. Learn to laser in place, to dash, immediately jump and get full momentum lasering forward, to retreating laser (run backwards and reverse laser). There are two ways to retreating laser: if you jump, then press back and then B, you get a lot of momentum. If you press back before you jump you'll stop about where you are and laser backwards. these are both useful. learn isai dropping (the sticky on the boards called hao to fazfall or whatever explains it).
get good at wavelanding on the various platforms. once you're good at this, get used to shine wavelanding: this is where you shine right below a platform, jump out of it, and then waveland onto the platform. this is also crucial in getting the most out of your combos, but can be left to practice until you have the rest of your basics down.
From there it's mostly learning combos and fluidity. run around and string moves together. shffl shine, shffl shine wd shffl, shffl shine wd back shine wd forward, aerial shine jump shine waveland, waveland onto platform, etc. take different CPUs to the different stages and combo them as best you can. improve speed and fluidity through practice, always assuming you can do things faster and more precisely. learn shffls with early and late aerials.
there's a lot of other tricks that are important but very situational, like ledge hop double lasers, shine turnaround edgehogs, doubleshines, etc. those can come later, in general.
...i think that's a pretty **** good list of what technical skills a falco should learn proficiency at, if i say so myself.
