I'm probably a bit of an expert on this subject (the amount of facial hair I have is my qualification)
Advice for would be threadees;
Don't pick the booth in the middle of the shopping centre. What you need ideally, is a nice little salon populated by ladies wearing hijabs. They've been doing this for decades, they've seen facial hair more like a full winter pelt, monobrows, hairy foreheads and everything else. Trust them.
DO NOT GO WHEN YOU'RE DUE ON. Just no. Never. Ever. Ever (ever, ever, ever, ever, ever.....) Mid month is much better.
Going in cold weather is a lot better than during a heatwave.
Tie your hair back.
Make sure any facial piercings are very secure - nobody needs a twisty bit of cotton to loop itself around a nose stud or a septum clicker.
Practice holding your eyelid down with the fingers on the same side and tightening/lifting your forehead/brow with the other - she needs to be able to get close and will stand on the side she will be working on. They'll probably say 'Hold please'.
Be prepared for an lady's bosom to be closer to you than you ever thought possible without a prenuptial. Not all do, but some presumably need to get close to see what they're doing.
When it comes to round your lips, you'll find it slightly less 'stingy' to use your tongue to stretch the skin.
There is no way of mitigating the sting just under your nose. None at all.
Use your right hand to tighten your left cheek by pulling on your hair above the ears, like a facelift. Those buggers on your hairline really make their presence known.
You will realise that you were considerably hairier than you thought you were. And your pride in a remarkably high pain threshold was been irrevocably shattered.
They're used to people making a flapping gesture with their hands to get them to stop. They have a huge box of tissues for this purpose - they will probably already be getting one out of the box when you lift your hand.
You WILL cry. No ifs and buts. It's a biological certainty.
You can trust them to shape your brows in a flattering way. No accidents like you can have with wax or plucking. They will also likely stop and look at you a couple of times to make sure they look right. And they'll whisk out any grey arctic blonde hairs you spot.
Once they've finished threading, they'll use the little crane handled scissors to ensure the brows are neat and level.
They'll brush off more extracted hair than you ever thought possible.
If they ask 'do you want gel?' they mean do you want Aloe Vera gel. Say yes.
The best ones make it sting but don't press into your skin much - the less good ones will have you wincing as you feel each hair rip out. Make your skin tighter if you get the ripping (like bad waxing) feeling. You are more likely to get the rippers in the shopping centre booths.
Run your fingers over your face and jawline - you will feel any little hairs that have been missed. If they are under the skin, she might not be able to reach it - some may use a pair of needle nosed tweezers to get them, but not everyone will - but she will try and get those extras.
Your face will be red afterwards. If you get little red dots, they were too aggressive and you go somewhere else next time (like the hijabi shops I've already recommended twice). It should go within 5 -10 minutes, possibly a bit longer on the first go.
You will find that your makeup goes on like a dream afterwards - foundation, eyeshadow, everything.
It's worth every bit of the sting - never seen anybody do anything but say thank you and smile through the tears and pink patches because it does such a good job for so little money.