Start with the lowest strength which is I think 0.025%. Don’t be tempted to try anything stronger even though that sounds like a tiny number. Start off with like 1-2 times a week, at night time, on dry skin. Don’t use any acids or other actives on a tretinoin night. Literally use a pea sized amount. I tap teeny tiny amounts from the pea sized blob, like little dots on my face and then rub it in from there. Avoid the eyes, lips and crevices around the nose. Give it time to dry/sink in, then top with a good moisturiser. Wear spf on your face every day. You can build up your usage once your skin gets used to it and if you have no effects. Your skin can purge at first or get a bit peely. You can also ‘sandwich’ your tretinoin by applying moisturiser first, then the pea sized amount of tret, then more moisturiser. That can help if your skin is really sensitive.
Sounds like a faff but it cut down my skincare in routine to hardly anything at all when I was using it (I stopped for a holiday under a raging 40 degree sun and didn’t restart because I’m trying to get pregnant at the moment and vitamin A, which is what tret is, is a no no) and my skin looked a lot better for using it. Fresher and a bit glowier, but not glass skin glowy if that makes any sense.
You might like to try retinol or retinal first which is a more diluted version of tret. I’ve never tried retinal but I have tried The Ordinary’s retinol in squalane and I liked it. Again, start with the lowest number and build your way up.
It’s not a prescription only medication in quite a lot of other countries so no prescription will be needed for that site I don’t suppose! (I bought mine on a previous holiday, but didn’t use it till I got back!)