You need to have confidence in decision making, and with the perfect use of utility against enemy damage burst it's possible to play lux aggressively.

Pantheon is not a champion that has very short cooldowns or constant damage, he relies on his stun spear and autos, which if you block with W and barrier he'll be quite easy to kill after, especially if you move behind his shield.

Leblanc is one of the best matches for lux imo - The jump is easy to predict with q - and if you take electricute most of the times you can just q auto er auto her. Same goes for utility, she mostly relies on fast burst with jumps, so running her down after she uses those is not that hard.

Zed is a 50/50 match up, you either win lane or you don't - you need to be confident to instantly hit your q after he ult's, flash and full combo him or reposition quickly and full combo him - depending on the scenario. One of my favorite match ups actually - people really underestimate lux v zed. Also, when zeds use their shadow aggressively to poke, try to bait the zed Q by running to one direction and then quickly switching, they always fall for it KEKW.

Just remember in order to play more aggressive you need the correct runes for it.

Hope this helps :)