First thing I’d say is know your lines.
Your eyes look different when you’re reading cue
Cards taped beside your laptop. Other signs
You’re not prepared include inserting new
Text into Chekhov or actually choosing
A speech from Vanya in the first place.
I don’t even understand misery-musing
Russian plays, and I’ve done my face-
to-my-navel share of introspecting. None
Of us are old enough for that. All right–
Here’s the actionable counsel: when you’re done
Learning your words and gotten your images tight,
Open the door of your heart and say, “Come in.”
The gold of you shines when there’s nothing to win.

(And it takes forever to learn because it feels like you’re not doing anything.)

(And there’re about 58 other things you need to be good at to do a monologue well, but at 18 years old, start by laying off the Chekhov.)