Lux smuxi is a champion I play if it's a last resort, jk i play her quite often.
When i play mid lane, depending on the enemy, I focus farming with E's and autos, i only E if the enemy is by the CS otherwise i considerate it not worth it. I do not use Q to CS early because i need that Q in case a lovely enemy Hecarim (example) comes storming into mid lane, with my Q i can root the enemy/enemies and walk away to safety. If you get ally junglers who don't always gank, you will have to look after yourself, sure you can blame the jungler for being useless but do not write in chat or i will personally obliterate you.

Lux can be stressful because of her skill shots and her squishy-ness, personally i go into practice custom games of 1v5 to practice getting out of ******** situations, practice tool to practice skill shots, draft to try out builds with fellow real people because let's be honest, there is no way the bots are going to help you to learn prediction because only newbies will just walk into that glittery Q.

Towards about 20 mins, you should think about roaming depending on how you're doing in lane, do not roam if you have a strong enemy attacking your tower but follow them cautiously if they wander off down bot. I do not recommend going down river because their jungler could be with them and could easily take you down.

In team fights solely work on keeping allies alive while also throwing in an E or a Q if necessary because you cannot 1v5, it's just how it is, league is a team game. DO NOT HOG ALL THE KILLS! However i'm not saying to just play support 2.0, you need assists too to get that S+.

If you're being chased a good tactic is to Q as many enemies as possible and E to slow, it's not much but it can save lives. There has been many a time when i have been chased and i've been able to turn on them, but that doesn't happen very often so just be careful.