Just don't leave it plugged in and shoved under your pillow while you're sleeping. (Obvious? Sure, for smart people, not so much for others! LOL)
My charging cycles vary from day to day depending on my usage. I've gone to bed with my phone only at 45% and not charge it. I wake up and I'm down only (usually) to about 30% after about 6-7 hours of sleeping.
Leaving it plugged in when the battery is full doesn't hurt it. The phone and chargers know to switch to a "trickle charge" when the battery is full. You're totally fine. I used to do this ALL the time on my last 3 android phones.