Surround placement depends on the situation. If you only have 2 surrounds, then they should be at some location between your sides and behind you, so they have the best compromise between sides and rears. If you're using 4 surrounds, then you can move the surround speakers directly to your sides or slightly forward in order to have better separation from the surround-back speakers on the back wall.
With the same thinking, if you're doing a non-Atmos set-up, then the surrounds should be elevated at some height between ear level and the ceiling, so that they have the best compromise between surrounds and heights. If you have an Atmos set-up, then you can move the surrounds closer to ear level in order to have better separation from the height speakers on the ceiling.
Speakers usually sound best on-axis (aimed at the listener). Surround speakers have to follow the same laws of physics as other speakers. So if you're pointing your centre speaker at you, then you should point all other speakers at you.