I thought that was common sense not worth bringing up.
With TF2 I never assume what is and isn't common sense. Anything, up to and including how to move, is in question.
You're 100% right there! It's very easy to size up the experience and skill of a player just by watching them walk and move around. Good players have trained themselves to always be moving erratically, every touch of the WASD has purpose, and nothing is wasted. New players on the other hand are freqently holding still or moving in straight lines, are often confused and unsure of what to do or where to go, and aren't mindful of their environment; leading to funny moments where they walk into the insta-gib sawblades or off a death cliff.
There's also other benign skills that prove vitally important that you'd normally never think about:
Awareness: Probably 80% of the 'real' skill of TF2 just comes from awareness. Keeping your eyes and ears open at all times to gain a full grasp of what's happening around you. You won't be caught off guard nearly as often, you'll catch others off guard! You'll be mindful of good opportunities and where both safety and danger is.
Listening: This just ties into awareness, but I just want to mention that TF2 confers SO MUCH information through audio, it's nuts. If you really listen and pay attention, you can hear nearby players footsteps, and it's possible to track invisible spies this way. All classes have unique grunts and screams for whatever, so you can get a good idea of if they've been hit and are hurt before even looking at them. If you hear "I'm movin this" you know it's time to rush up and whoop an engineer's ass while he's carrying his sentry (or you might get unlucky and he was carrying his dispenser the whole time). Additionally, while heavy's slow movement speed is his 1# weakness, his 2# weakness is his minigun, because while it's the strongest weapon in the game by far, it is also the NOISIEST. When you're revved up, the whirring and firing noise drowns out other nearby noises, so not only are you probably being tunnel visioned trying to shoot something, but your ears are being covered up as well! It's another thing that makes it easy for spies to just decloak behind you, because otherwise they'd be heard out. Having a good set of headphones is a must in this game, a must must must.
Discipline: This is a very dire and serious trait to talk about when discussing a videogame, but TF2 demands it so often and so severely that it can't be ignored. When firing a weapon like a rocket launcher, it is VERY tempting to just spam at people's feet and hope for the best. When using a weapon like the SMG or Pistol, it's very tempting to just spam into someone's general direction and hope for the best. When you're caught off guard by a pyro and taking damage, it's very tempting to panic and run away. TF2 is a game that requires "Hard Decisiveness", in that in a split second you have to decided what the best course of action is, and then stick to it, not just what your emotions tell you is correct. You have to be always mindful of prediction so you can score directs with rockets, always mindful of spread and the location of the crosshair and the enemy so pistol shots hit, and being able to size up an enemy in an instant so you can dedicate yourself to killing them even if you're being rushed down. Someone who is very disciplined will hit more shots because they can wait for a good shot in a stressful situation, will not panic when surprised, and can make hard choices when pressed for time.
Interpersonal Skills: Naturally, in a teamwork-centric game like this, being able to both communicate and cooperate with your team members is of vital importance. As obvious as it is, alot of people don't have interpersonal skills, they are deliberately nasty and stubborn. A bad attitude holds them back when oftentimes the key to success is found in being able to cooperate with those around you.
Thanks for reading my impromptu powerpoint presentation, have a nice day now.