I can't speak much for 50+ or 8-man content as I've only done "ROFLstomp" aka Operation Archon. However, I can recommend a few things.

- Flexibility: By now, you will have likely learned how imperative it is to place your fairy so she heals efficiently. This is an indisputable truth. Your PT members will also likely prefer you use Selene for her speed buffs. Her ability to increase overall DPS is also an indisputable truth. However, YOU should be the one to determine what is best for any given situation.

- Obey/Sic: Don't fall into "always keep fairies on Obey". This is mostly (not always) true for Eos, but not Selene. Remember, flexibility. Selene's AI is actually pretty good, and she is really fast. Plus, due the conditions that need to be met for her to cast, none one of them really go to waste unlike Eos. Learning the AI of your fairies is key to knowing when to have them on Sic and when to have them on Obey, and the situations that will serve you best with each. For example, learn the conditions that Selene will cast Fey Wind, Fey Caress, and Silent Dusk. Don't be afraid to alternate these commands even during a single battle.

- Micro management: If you are having trouble with this, I recommend doing challenging solo content to practice. Keep in mind that you can make easy content more challenging by nerfing yourself. Fight mob after mob after mob until accessing and using your fairies toolkit is transferred over to muscle memory.

- Placing your fairy: The place command, honestly isn't much different than setting up Sacred Soil or Shadow Flare. If you can do those, you can place your fairy. Again, practice in challenging solo content. Also don't be shy about summoning a different fairy during battle if need be (hope you have swiftcast). If SC is on CD or you don't have it, then cast without sending her away first to ensure she still heals during the casting duration. I believe you also have access to Embrace during this time, assuming your fairy is on Obey.

- Healing is your priority: Don't ever forget this. Lacky scholars blame their faires for KO's and wipes. Don't be that person.

- Succor is AoE galvanize, not AoE heal: If you're casting succor after big damage, you're late. If you're spamming succor to repair said big damage, you're wasting MP. Galvanize should be up to absorb some of the damage, and then reapplied after it is wiped out for the next mob rotation. Sacred Soil + Succor is serious mitigation for the entire group, while Rouse+Fey Illumination+Whispering Dawn will get HP bars back up in no time.

- TRUST your fairy: They are REALLY good at healing. Allow them to do it while you fish for Adlo crits on the tank.