It depends on what class you're playing against, but with scouts you should move predictably/strafe normally but switch up your movement just when they're about to shoot. Against soldiers you can really tro to mind game them. I wouldn't be able to tell you how to be good at that though

there really isnt any great advice for this question other than to practice. try playing dm and never play high ground/never rocket jump, which will force you to work on your footwork and be unpredictable on the ground. play scout in pugs, many of the concepts of being unpredictable as scout carry over to other classes but scout will force you to learn them more constantly.

Sometimes when I am fighting a scout on low health and I cannot RJ away, in the middle of dodging with A-D I like to hit duck and stand still for a split second and then continue to dodge with A-D again. Can't tell you the number of times it allowed me to get a kill I wasn't supposed to get because it fucked up the scouts aim.

As far as soldier vs soldier, if you are playing against good players, most soldiers are going to hit you for at least some damage when engaged. Surfing that damage for speed is the best dodging possible but if you want to work strictly on your DM movement I would get a friend and MGE on ENDIF. In the old days we would not go for airshot kills to win. You simply help each other work on mid-range DM movement and surfing damage without having to worry about killing each other.

surf damage = gg

when you're fighting a scout- rocket jump away

ammomod mge > unbind jump > focus solely on strafing and predicting opponent dodge
Learning other player's movement patterns inherently makes your movement better

Pay attention in games/mge/whatever

If you're playing against someone with good movement and having a hard time landing a rocket on them, watch how they move and what about their movement throws you off. Then copy that into your own dodges

!add nosplash

soldier movement is mostly like every non-scout classes movement

surf rockets

walk away from where projectiles are going.

put yourself into the mind of your opponent and envision where he expects you to go, then don't go there

pulling out escape plan for a second and jumping to preserve your speed is a good trick to get an extra boost at the cost of a slower reload

spam null movement script and don't jump vs hitscan

don't always walk directly towards health kits

also practice 11 damage rocket jumps and using rockets to prevent fall damage

try

Play good players in ammomod. You'll get a feel for the nuances of dodging rockets.

Learning scout helps too.

Always when i grind mge on ammomod, i try guess where my enemy will shoot , just guess what you would do in his position. Slighty before he shoots the rocket (you can guess when he shoots his rocket, he probably wants to shoot the earliest time possible) i jump into the other direction trying to dodge the rocket. With this you can actually take 0 dmg from rockets, it just needs some practice and experience.

tight strafes vs scouts. you can't really isolate movement from the rest of your game. often you just want to move for aim or for position. you want to bait the scout to walk into your rocket if he wants a good shot. youre not neo, youre a fat soldier waddling at 240 units/s. but a/d spam works sometimes.

larger strafes vs soldiers. jukes before he shoots each rocket. jump more and surfing is obviously good. you can also throw in some w and s, forward and back can really fuck up rocket aim. if you need to 100% dodge a splash rocket its your only chance.

swing ur mouse around like an idiot to make ur model funky

This but also hide behind walls

Like Aim Said, surfing will win for you a lot.

Surf Rockets, Pipes, Stickies, and scatter gun shots. As long as they aren't into the ground it is useful.

and just be really unpredictable, I don't mean autistic, but if that works, go for it.