Forearms arent particularly painful to have tattooed, some do feel discomfort as most designs will wrap around onto less fleshier parts of the arm.
I'd go with one of those as your first, clavicle wont be "Painful" but start with the easier of the 2 areas, forearm being that.
Any other advice?
Please do your homework regarding artist, you may find one specialises in certain areas. Make sure its a clean and reputable place. Ask to see their previous work.
Setting up an appointment to speak to them first is always a benefit, most will charge for this, and take the price off your tattoo (saves time wasters, but not all take the money off, so check)
make sure you are 100% happy with your design before going ahead, dont be afraid to make changes to the design before appointment day.
Eat a smell to medium meal before you go, dont drink alcohol the night before, and follow aftercare instructions properly.
Leave a decent healing period between tattoos, let your body heal properly before getting another, including any touch ups (it does happen and not a reflection on your artist, especially with areas of high detail, you cannot overwork an area so its best to leave it and go back to it after a couple of weeks healing)
relax and enjoy the process