I have a 500D and recently took some tack-sharp night shots with the 24-104mm f/4L lens - should be of similar quality as your 70-200. Here's what I did.
- Got myself a new tripod (well I got one for Christmas). I used to have a cheap tripod, and there's a huge difference. Especially in windy conditions, the cheap tripod cannot take sharp pictures. Also if you have a center column in the tripod, don't extend it unless you have to. Extend the legs instead.
- For focusing, I switch to live view. The focusing in live view is more precise. Also, you can zoom in 10x in live view and make the focusing manually. Then switch off live view, and change the lens to manual focus, so you don't accidentally move the focus point when taking the shot.
- Turn off image stabilization on the lens (some lenses will introduce movement when trying to counteract it, some lenses can work with IS on tripod, but if unsure, turn it off)
- Turn on mirror lock-up. That means you have to press the shutter twice, first time locks up the mirror, second time takes the picture.
- For most of the pictures I simply used the camera's build in timer function, allowing the camera to stabilize itself after pressing the shutter button. But a cable release is better.
A note on mirror lock up. When hand holding the camera, your hands will absorb the vibration caused by the mirror movement. But placing the camera on a rigid tripod, the vibration will bounce back into the camera. The amount of vibration is very small though, so for longer exposures, enabling mirror lock up will not have a profound effect.
Also for very long exposures, using a cable release, or build in timer may not be necessary, as maybe you will get vibration for the first 1-2 seconds of e.g. a 20 second exposure. But if you want the sharpest possible pictures, you should.
The pictures however are not noise-free. The body has a cheap sensor that does not perform well in regards to noise. When shooting long exposures, the sensor will heat up, and a heated sensor generate more noise. That is also the reason why you should only use live-view for focusing.
Also note that if the subject is illuminated by tungsten light, there will be very little image information in the blue channel, or in other words, the blue channel will be very noisy. When adjusting the white balance, you will amplify the blue channel quite a lot, therefore also amplify the noise. Most of the tack sharp night shots I took got converted to BW which produced significantly less noisy pictures, as I could skip white balance correction and take image from the red and green channels.