Your skin will probably be a bit sensitive at first, so if you use any exfoliating acids etc maybe scale back a bit while you get used to it, and just generally make sure the rest of your skincare is really gentle. And yes, definitely make sure you’re using a decent SPF (at least factor 30, broad spectrum).
You don’t always get peeling/redness though, I didn’t. What I did get though was spots, so that’s something to be aware of. I’m not really acne prone, but I used to get spots when I’m my period was due. The retinol brought that all to a head, so for a few weeks my skin looked worse, but then it passed and my skin has been clear ever since. So if that happens to you keep the faith! Spots can also be a reaction to the product itself though, the way I told the difference was that the spots were on my jaw/chin, where I would tend to break out anyway. If it’s a reaction to the product they would have been in places I didn’t normally get spots in.
As well as the concentration of the product, the base it’s in can make a difference to how well you tolerate it, so an oil is generally better tolerated than a cream. But I didn’t know that and I started with a cream and it was fine! Just go really slowly at first, just a couple of times a week, and only step it up and use it more often if you’re tolerating it well.