Salmon and tuna are good meaty fishes that will grill well. Most other fish is too flaky to grill.
You don't need a whole lot of seasoning. Salt, pepper, garlic, parsley and olive oil will take you far.
Marinating is probably a good idea - it will make the fish cook faster so it's done in the middle before the outside is completely charred. Lemon or lime juice is a great base for a marinade. But to be honest, salmon and tuna are fish you can eat raw, so you could just buy them very fresh and experiment.
