We're going to Krka falls in a week, so we expect it to be crowded and hot.

With this in mind, I've seen reviews that suggest we park at Skradin and get the boat.
But have also seen recommendations to start at Lozovac and go counter clockwise.

Which would you recommend?

-I'm not sure if I'm misunderstanding, but at Lozovac and Skradin two sides of the same place? Or two different lakes entirely?? I've read that we 'should' visit Skradin, Lozovac, and Roski Slap.

Can someone please help me get my head round how to plan the day?

We have a full day there, with a car.

Thanks!!!!

I think you would do well to look at google maps. Or, for that matter, the official KRKA National Park web-site:
https://www.npkrka.hr/en_US/posjeti/ulazi-u-park/
Skradin and Lozovac are different locations near the lowest part of the park. Lozovac looks closer and seems to have free parking. I don't know how easy / difficult parking in Skradin would be, but I'm sure you can investigate. If you start in Lozovac, you could probably skip Skradin if that's what you want -- or not. Your call!

I started and ended (by bus) in Skradin, which I found a pleasant little town -- but that was years ago; I have no idea what it's like now. FWIW, I walked a well tended, wide, gently sloping path from Skradin to the entrance to the park near Skradinski Buk, then walked to Roski Slap on the right side of the water (facing uphill) and back down on the other side. I then took the ferry from the park entrance back to Skradin. In retrospect, I wish I'd taken the ferry from Skradin -- I had wanted to visit the monastery further upriver, but I got there just minutes too late for the last ferry to the monastery. Again, it was years ago, so the timing of various modes of transport have probably changed. (Or I could have walked faster. Sigh.) If you are interested in seeing the monastery, consult the schedules.

As for which direction, I can't help. I would say that I prefer to go WITH a crowd (at my own pace) than AGAINST a crowd (which means I'm always trying to wend my way between people holding their cameras to my face). Perhaps the people at the entrance to the park can advise you?

As for what people say you "should" visit -- ignore them. Visit what interests YOU.

The Krka falls are glorious -- enjoy!