Use bib shorts, rather than cycling shorts.
Don't set your seat too high (or too low).
Watch GCN on youtube, lots of good stuff for learning on there.
Just do slow and steady rides, so you don't burn out your legs as this takes longer to recover from. Try a higher cadence (lower gear/ peddling/ spinning faster), this will work your lungs and get you fitter and is easier to recover from, for riding multiple days in a row.
If you're riding for longer than 60-90 minutes take some sort of snack like an energy bar/ energy gel or something like a flapjack. Most people can hit "the wall" after like 60-90 minutes at high intensity. This is less of a problem if you're going slower as your body can use a bit more fat for energy, rather than relying on carbs.
Could try controlling your calorie intake with an app like myfitnesspal, but make sure you're eating enough on the days you're riding.
Use Komoot for planning routes, and get a cycle computer like a wahoo bolt or the Garmin equivalent (don't put your phone on your handlebars).
And most importantly, sunglasses go over your helmet straps, not under