Depends on the type of fish, I eat fish twice a week and always try different kinds of fish and different ways to cook them. I cant even count the number of recipes I've tried but simply adding lemon is my favorite, and easiest.
First you have to find what kind of fish you like, or is available, I've tried so many different types and my personal favorites are mahi mahi, red snapper, branzino, tilapia and cod in that order with mahi mahi my favorite. Red snapper is smaller so little harder to cook than mahi mahi but sometimes it does taste better. Also only get fish that have the skin still attached, either fillets or whole fish.
I find the best tasting fish is cooked on the skin in the grill outside. Preheat the grill, put some oil based non stick on the grill then put the fish on skin down. I always follow the rule my fish market told me, 8 minutes of cooking per inch of thickness, and check it a couple minutes before its supposed to be done. You'll know its done when you try to bend it and the fillet breaks (not the skin).
After its done put lemon juice on it, either fresh squeezed or even better is the little containers of natural real lemon juice.
Now the other option which adds another step but is my favorite is to take the fish off the grill a little before its done, put it in the oven at about 350, put aluminum foil on a baking sheet and put the lemon juice on top of the fish and in the aluminum foil and add a lemon wedge ever 2 inches and cook it for about 5 to 12 minutes depending on the thickness, 5 minutes being for red snapper.
You can cook the entire thing in the oven like this as well and it tastes good but I prefer the grill.
The only things I'll put on top besides lemon is I'll make a sort of mix that I thought of myself, I cook spanish rice and put olives and baby spinach leaves in it and put it on top and on the sides of the fish.