Audio quality is the single biggest difference between amateur and professional-feeling lessons.
Get close to the mic
A cheap microphone 15 cm from your mouth sounds better than an expensive one across the room.
Treat the room, not the walls
Soft things absorb echo: a sofa, curtains, a rug, even a duvet hung behind the camera.
Turn things off
Fridges, fans and air conditioning hum quietly in the background. Switch them off while recording.
Record a test first
Record 30 seconds, listen back on headphones, adjust, then record the lesson.
Keep levels steady
Aim for your voice to peak around -12 dB. Too quiet adds noise when boosted; too loud distorts.