My scripts can be a bit inefficient but they work. Just define variables like "stance" (left or right) and "act" (run, jump, stand, etc.) based on keys pressed and then switch animations and do movements based on what the variables are every frame.
Meaning, the first half of the script would be an "action plan" where a bunch of questions are asked about what keys are being pressed and defines variables based on the answers, and the second half is the "execution" where it reads the variables and places the right animation and does things like this._x += 15, and so on.
What I mean by "places the right animation" is have every animation like running, standing, jumping, etc. all as their own MCs, then place them all into one MC, each frame being its own animation, and put the script on THAT MC, telling it to gotoAndStop(desiredAnimation);
Get it? This is just how I do it. There's probably a much more efficient way.