Had been on a cleanser+moisturizer combo before going to sleep for most of my adult life. Very liberal use of sunscreen.
Came across some research on different retinoids, started with a medium strength retinol serum (The Ordinary 0.5% Retinol Serum in Squalane) before moving to a higher strength retinol serum (The Ordinary 1% Retinol Serum in Squalane). Three drops on a dry skin after using a cleanser, one to each cheek, one to my forehead, spread evenly. Moisturizer applied after letting it settl
Highlighting the existence of different retinoids is good. I have used retinol serums and a tretinoin cream (not at the same time). Retinol products are the most popular in the retinoid skincare category, and are sold over the counter, so reading specifically about them might be worthwhile.