Of course there is flash when all else fails, but on-camera flash tends to be a rather ugly light. Shooting without flash, shutter speed is critical to eliminating blur. When working in low light, use the widest aperture (numerically lowest - f-2.8 is wide - f-11 is small), and set whatever ISO sensitivity will give you a shutter speed sufficient to stop both camera and subject motion when shooting in aperture priority(Av).

The shutter speed needed, depends a lot on how steady you can hold the camera. Since digital incurs no costs in film or processing, practice and check your results to determine your own baseline. It is much easier to get good results at the widest part of a zoom than at the telephoto end. Check at both the wide end, and the greatest setting you will be using.

Don't wait until you are taking pictures you really want - use a piece of furniture or other object in the room as a subject, and delete the shots once you have your answers. Realize that in very low light, with the lens wide open and the camera set to ISO1600, there may not be sufficient light for consistently good results. In this case shoot lots, and hope for a few sharp ones.

Monopods are available at reasonable prices, are very mobile and give you enough support to work in considerably lower light. You might consider one - much cheaper than an image stabilized lens and way less awkward than a tripod. Anything that you can rest your hands or the camera on, will extend your ability to shoot at low shutter speeds. Even sitting down or leaning against a wall will help. Through practice, you may also learn to hold steady at speeds lower than now.

You might also consider Canon's ~$80 50mm f/1.8 lens. For the money, it's a good lens and very fast.

Quote:
You might also consider Canon's ~$80 50mm f/1.8 lens. For the money, it's a good lens and very fast.

You took the words right out of my mou.... um, off my keyboard, Paul!

Assuming that frey got the kit lens with the camera, most of those are pretty "slow", meaning they have a smaller aperture and don't admit as much light at their largest possible setting.

An f1.8 lens like the "Nifty Fifty" can really make a difference, with an extra stop of speed, maybe even more, depending upon the lens that's now on the camera.

Good suggestions from Larry, too. A lot of it is just practice.

The "rule of thumb" regarding shutter speed with 35mm film cameras was always that most people could safely handhold their camera at a shutter speed that's the reciprocal of the lens' focal length. In other words, if they have a 50mm lens mounted, they need 1/60 (closest to 1/50 reciprocal). With a 20mm lens, you'd set 1/25. With a 100mm lens, you'd choose 1/100.

Still applies although some people learn to hold the camera steady enough at even slower speeds, and, more importantly, you have to factor in that the lens acts like it's 1.6X longer on today's APS-C cameras. So, you might use about 1/80 with a 50mm lens now, on cameras like the XTi. When i doubt, use a slightly faster shutter speed to be sure.

There are lots of good books about photography in general. And some specific by model, like the "Magic Lantern Guide for Canon XTi", which picks up where the user manual leaves off.

Cheers!

Do not feel bad, after 30 years I still get the occasional blurry photo. The best thing you can do is practice and get a good book on General photography. To become really good and make photographs the way the pros do will require effort on your part. I have seen countless people grabbed a XTi or other entry-level camera and decide to go into photography as a business because it looked easy. Do not get me wrong the XTi is a good camera a matter of fact I just got through shooting a college theatrical and the XTi was the secondary camera I was using. On the other hand many people will go out and buy a 1D Mark 3 and come back with pictures that are blurry, out of focus, and improperly exposed.
Practice, read the manual, get a good book. That is my advice.