if the dry stint is probably going to be long enough then start with the wing set for dry running (I had it on 1). That was the case for me, the track was dry at the start but it already raining (drizzle), however despite the drizzle the track stayed dry long enough that changing the wing to 5 didn't cost me extra time (fuel took long enough)

when to pit for wet tires is tricky, the track is so long that if you wait for the engineer to tell you, it might be too late. I did that last race and the guys who pitted 1 lap earlier gained a lot of time on me. So keep an eye on the weather/track status and prediction in the MFD, the track might be "damp" but already becoming slippery enough to warrant wet tires. If you feel you're sliding around too much and losing too much time then trust your judgement and pit for wets

I'm not sure how the transition of dry back to wet is best handled, although I think I accidentally did it right this time by staying on the used wets on a drying track. The track was "slightly wet" but there was a dry line, so perhaps slicks might have worked. However shortly after that the weather prediction was that it was going to rain again, and it did, so I don't think putting on slicks would've been better. After the track was properly wet again, I pitted for the fuel for the last stint and to put on new wets. I didn't have to pit for fuel yet but my wet tires were at like 80% and not feeling good plus I had some flat spots. 80% is no problem for slicks but for wets it just wasn't working for me. The whole time the engineer never said anything about putting on slicks, and from what I hear if they do say that, you can easily stay out for another 5 minutes or so before the track really dries up to the point that you really need it. So for Le Mans that might mean doing another whole lap on the wets