The Harry Potter areas get absolutely packed, so you may want to hit them early on or later in the evening. The ambiance of Diagon Alley (Universal side, whereas Hogsmeade is on the Islands of Adventure side) is gorgeous when it gets dark, so if you can stay late enough, visit that section at night.

The Hogwarts Express that goes between the parks (presuming you have 2-park passes) is nice, but the line can get VERY long for this. Even though it can be a long walk, you can sometimes just exit the one park and walk all the way over to the other park, faster than it would take to wait for the Hogwarts Express.

I love these parks dearly (spent many a day there with my kids back when we had annual passes for a few years, ~2015-2017 or so), as they have great little kids areas too); now that things are close to returning to normal I'm looking forward to grabbing passes for the family again!

They've been making a lot of updates to the Jurassic Park area in Islands of Adventure and I believe their new roller coaster is opening in early June.

rwmech5 mentioned Mythos, that's on the Islands of Adventure side and it is indeed very good. In Islands, we also enjoy eating at Confisco Grille, very good food there too. (We typically spend more time on the Islands side.)

One more tip: naturally, you'll want to try an (overpriced) butterbeer in the Harry Potter areas, they're delicious. If you're in Hogsmeade and the lines at the butterbeer carts are too long, you can slip into the Hog's Head pub and order them at the bar too, this is sometimes shorter than waiting at the cart. You can get them frozen (like a slushy -- great for summertime), regular (standard soda consistency), or if it's cold out you can get them made hot like a hot cocoa.