Yeah, I'm new to DSLR, too, so I feel like I got pretty lucky my first time on manual.
Everything I read said to first of all be sure to use a tripod, and a remote if you have one so that you don't even have to touch the camera once you have it focused, framed, etc. Well, I don't have a remote (or whatever it's called...), so I was just very careful to hold still next to the tripod.
Most recommendations I saw were for ISO 100 (or maybe 200), and to have the aperture set somewhere between f/8 - f/16 or even f/22. I used f/16 the whole time. And I went with the Bulb setting for shutter speed since that was recommended, too. I think it's because you then have manual control from shot to shot over the shutter speed without having to reset it on the camera every time. So I would count as I was holding down the shutter. Now my counting was probably not very precise, but I'd guess I was holding down the shutter anywhere from 5-25 seconds. I tried to vary it. Most of the time I was probably in the 12-15 second range. I just tried to be very still as I was holding down the shutter to reduce the blur, even though I was using the tripod. Oh, I did read somewhere NOT to use the VR on your lens if you're using a tripod. Wasn't and issue for me since I was using the 18-55 lens. Maybe that's what happened when you used your 200mm lens?
We lucked out and had perfect weather, too. It was a clear night, and not too hot. Plus we ended up in a fabulous spot for watching the fireworks this year.
HTH! Good luck tonight!