Just let the juices of each fruit marinate together overnight, or use a mixture of whatever you like best as a "dressing".  We just like the natural juices, but once I made up a dressing of olive oil, lemon juice, a bit of water and a dash of nutmeg and everyone liked it.  Very simple dressings are the best, if you're going to use one, because otherwise you drown out the taste of the glorious summer fruit medley.

This stuff is great made however YOU like it best!

https://www.tasteofhome.com/article/how-to-make-fruit-cocktail/