If you're new to grilling fish, a foil packet is going to be the most idiot-proof way to do it, and keep you from breaking it up when you try to flip it and dropping it into the fire. I agree with our Italian friend to keep the seasoning very simple. I'd go with a very light drizzle of olive oil, a pinch of salt, and then serve lemon wedges at the table for squeezing.
If you want to grill openly, just gut, scale, and de-bone the fish. Leave the head and tail on. In the gut cavity, do your light seasoning thing. If you're not going to take the minimalist advice, then in addition to a bit of oil and salt you could put in some very thin lemon slices, or very thin onion slices, or very few fresh herbs (just one)--like couple sprigs of thyme or rosemary. But still very light, very simple, just one thing. When you're grilling whole this way, when it's time to flip, you can just roll the fish over so you don't screw up and break it up.
If the head and tail freak you out, you can cut them off, and open up (butterfly) the fish so that it lies skin-side down and flesh side up. If you do it this way, and it's thin (less than 1" thick after it's butterflied), DON'T FLIP IT. Just cook it covered till done through. If the skin sticks to the grill, so be it -- the flesh will come clean off the skin with your spatula. If it's more than 1" thick, then it's probably so big that you're doing BIG fillets because the whole fish won't fit on the grill. In this case, you're going to have to flip it WITH CONFIDENCE. But if it's that big there's less of a risk of botching/breaking it.
Personally I eat my sashimi in sushi bars, and wouldn't attempt the raw or extremely rare thing. But if you go for the seared/rare thing, you're going to have to be confident enough to flip it. Oil it, hot grill, maybe 2 minutes on side one, FLIP WITH CONFIDENCE to side two, 2 min. more, done.
If you're going to try flipping, or if you just want to make it a little easier on yourself, line the grill with heavy duty foil, and oil it, before you start. That way you're not going to spill broken fish between the grates.