my friend taught me that you can try to take advantage of the "delay x seconds to take photo" function on your camera.
when you press to shoot, your camera will move down no matter how steady you hold your camera. Therefore, use that function, after you press to shoot, you still have time to hold your camera steadily.
Of course for best result, you need to use tripod. You need to use manual function of your dslr and try to change the aperture or the shutter speed.
I am just an armature so those are little findings I found over the past few weeks..
I mostly shoot night shots without people in them so I dont usually use a flash. I set the ISO to 100, f16 and let the camera choose how long the exposure time, then I check the picture, if it's too dark, I'll increase the time but since the XTi has a limit of 30sec, sometimes I have to use manual mode and use the scroll wheel to set it to "bulb" which will let me set the time over 30sec.
Besides using a tripod, I suggest you get a remote control, I use the RC-5 which cost $20. It will let you shoot without touching the camera causing shaky, blurry picture.
For night picture with people in front, you'll need to use flash. To cut down the time people waiting in a long exposure, high iso and fast lens would help. I also set the flash to second curtain.
One more suggestion, take some time to practice before you go. good luck.
In general, keep your iso as low as possible, step down the aperture. ( ie: F5.6 or F8 or even F11 ) and use longer shutter speed. Of course, use tripod.
For night portrait, then just set to whatever manual setting, and ok to use higher iso such as 800 and up, and slightly bigger aperture such as F4 etc ... and fill in flash. (external flash) and you dont need to use tripod at all. ( wont hurt to use tripod, but hassle )
Or just set your camera to slow syn as dax said, or night portrait mode.
Unless you are trying to get the best best photo possible..! Personally, I would recommend using approx ISO400, so that the wait time isn't as long.. either because you have limited time, or because you want to review them..! Then.. if everything turn out to be as perfect as you want.. you can always change your ISO back to ISO100 for better image quality (less noise).
Use Aperture priority, pick your aperture anywhere between f/8 to f/16 depending on your subject! When you are going to use your flash, just make sure your camera doesn't automatically set your shutter to 1/60.. !