This is what I did when I played scout on steel but different playstyles work out better for everyone so you should experiment and just do what works best for you!
Pushing A: go to A and cap it. 99% of teams won't pressure it at all, just make sure to check for random hiding spots.
Pushing B: I almost always did the bonk strat to push their players off of the high ground balc thingie on B, what that is is just using bonk and then running up the stairs, body blocking spam in order to get your players space to walk up behind you, and then go into the cubby and kill the teleporter exit that is normally there. This gives your players who want to walk through main a ton of room and if you control that area after ubers fade you should be in a pretty good spot to win B (Credit to bv for thinking up of this strat which is now really common).
Pushing C: the #1 important thing about pushing C is taking control of wishbone, as that allows you to pressure E point, force their combo to rotate off of C, and then take C mostly for free. To help with this I like to bonk through wishbone to bait out sticky traps/demo spam/their sniper's shot, and then after we control that just pressure E cap until they rotate.
Pushing D/E (most teams just ignore D for pushing): I find that there isn't much you can do for these points besides just play with your combo and help teamfight and make sure to get captime any time you safely can.
Holding A: you can hide on A point and try to contest cap/get a random kill as you will spawn in time to help hold B 99% of the time, but it almost never really does much for your team, it just has very little downside. Usually I think just positioning yourself on E to watch for rotations or on B to help with any form of early sac wave is better.
Holding B: I think this mostly depends on how your spy wants to play it, if your spy doesn't want to just sit cloak and daggered on A doing nothing but call where their team goes (be it onto E, into dropdown, or back into spawn) then you're the best class to sit in the E spawn door and call where if they go into lobby/onto E. If they send their flank to pressure cap you're one of the best classes to rotate as you can just sit in the E spawn door and spam cleavers at their capping players. However unless they're committing players into E you really want to make sure you're in position to help with the teamfight that will happen on B.
Holding C: this point is kind of weird as scout, what I did was sit on cliff, calling anyone who tried to push that direction, and if they didn't send anyone I would flank into B from cliff and try to kill their teleporter exit/win a 1v1 vs a spawner as you should be able to 1v1 most classes on that open ground or just back out easily if it starts to go bad for you. The other big option is holding E/lobby, which I think is good but requires you play with your soldier/pyro (depending on which you commit to flank) because winning DM fights as scout in such a confined space is relatively hard.
Holding D/E: as soon as they cap C I try to be in position in spawn to call anyone pushing through death hallway, as if they're able to push that by surprise that can completely catch out and wipe your team. A lot of what I try to do is just be in a position to call where their players are and where they rotate, while being close enough to my combo to rotate for DM fights. Getting an early call on if their combo rotates wishbone is really helpful for your team, and can definitely make the difference to allow you to rotate your combo quick enough to stuff them in the choke. Also, if aren't in control of lobby it's important for you or your spy to be in position to rotate onto A and kill their sniper if he is in A window, as an uncontested sniper in A window can basically just win their team complete E control.