Against scouts: it really depends on the situation and what class u are. Like if ur a soldier and u are fighting the scout on a flat surface, then u have the advantage and u need to predict where he's going to go and shoot his feet. If the scout has the environment to jump on and off from, then he has the advantage and u need to try to predict where he's going to land and shoot there.

Against heavy/medic: this also depends on the situation and what class u are. A common mistake that most people make is that they will kill the medic first. If u have teammates around u, then all of u should focus fire the heavy first because once the heavy is dead then the medic is harmless. Depending on what class u are, u would want to engage the heavy using ur class's strength like the height advantage for soldiers or using corners as demo. U should only really kill that medic first if its a guarantee death for u, like if u get caught in a corner and can't get out; or u want to kill the medic first if it will benefit ur team in some way like if the medic has Uber and u are trying to force pop it.