Never really had a sticking problem. Sticking tells me you are leaving it on too short or too long. That may not be helpful but if you try to get it off and it sticks but does not fall apart, you aren’t cooking it enough. If it falls apart and all the little pieces are stuck, you left it on too long.
I will note that I cook fish skin side down, NO FLIPPING. About 6 minutes, 8 if it is really thick, 4 if not.
You’ll get a feel for this. In the meantime take a fork and gently, gently, see if you can get the fish to flake while on the grill. As you are cooking from the bottom up, you will be testing the medium to rarer portions. The second it seems to be coming apart, get it off and let it rest a few minutes, serve.
The skin side down, no flipping, was my reaction to flipping fish and having them fall apart. Not only does it prevent that, but the skin gets consistently crispy, and I feel I have more control as I don’t need to open the grill, causing cooling off, flip and restart the timer. My fish is now perfect from the grill.
The less you handle it the better. The skin also helps, maybe??, with the sticking aspect. If no skin, just pick a side to have down and go from there.
I DO flip scallops (U10, 60 seonds a side) and shrimp (no shell or tail, 90 seconds a side). I do not flip fish filets, lobster tails (shell side DOWN 8 minutes for 6oz tails). I never do fish steaks, I like filets better. YMMV.
I note that I have cast iron grates and do fish at about 425F.
For a herb mixture? I don’t have any special one. Always salt and pepper. And maybe that’s it. Sometimes I go with a crushed sundried tomato powder. Sometimes some garlic powder. I do a LOT of dry rubs for fish, rarely a wet marinade. No clue why, that’s just what occurrs to me and sort of one of my kitchen specialties. I’m working on rubs from around the world.
You might lightly oil your fish to keep it from sticking. I’ve not found that need, yet. But I don’t see the harm.
I’ll also note, just try it. Not with a date of course the first time. But practice practice. The no flipping was after 2 summers of working with salmon trying to figure out why I was inconsistent. I grill 300+ days a year. It just takes practice, some creativity and asking questions when something seems odd.