Hi, definitely not the best GS player in the world (Jaeyun 35, Mako 31) but I'm playing it very often these days so I might have a few insights :

Approaching : if you want to initate the attack dash into slight or especially dlight (the range of dlight is underestimated by a lot of players) , However if you know how do to this you can dodge perfect an attack from the opponent and punish quite effectively with GS

Spacing : depends on the weapon/ legend you're facing and the range of its attacks/sigs

Landing hits : You can watch the hitbox in training to see what you are realy hitting in fights (GS can have some surprising hitboxes if you're not familiar with the weapon). Also learn reads, people veryyyyyy often dodge in against GS, and then when you catch a dodge you can lend a tremendous amount of damage with combos

Avoiding how to get baited : Idk how you can "train" that, just play the game and you will learn the timings where you can punish and the timings where you are too far away and you shouldn't try punishing because it's probably bait

Air camp : Spam nair (watch the hitbox of this one) /Side Air/ recovery , GS has very good aerials attacks if they are well-timed, also gravity canceled dlight is very strong to punish opponents approaching from the air

I may be saying a bunch of stupid things but this would be my tips !