I've learned from experience that when taking photographs of people, even if they're standing still, I use 1/125th and faster to ensure I freeze any motion...theirs and mine. If possible, I'll use 1/160th for 'insurance'. One might think 1/80th is fast enough to freeze motion but I've learned that people may twitch a little bit, tighten a leg muscle to hold position, etc, and the image will blur as a result. As I get older, I'm also noticing that I move the camera a smidge while pressing the shutter, and have to correct a slight tilt more and more often. The cost of being retired, I guess. Another lesson learned is to set the AF Drive setting to 'AI Servo' so the camera will track any minor movement and stay in focus. It seems counter-intuitive since your camera has a 'one shot' setting. 'One shot' is for non-moving subjects like buildings, parked cars, and mountains. AI Servo for anything that moves...people, pets, cars, etc. I still forget to switch back to AI Servo after shooting at a car show... Given the lens you have, even at the widest angle (18mm), f3.5 will be quite limiting in how bright things need to be. As you zoom out, the minimum aperture effectively gets smaller to f4.5, requiring even more light to get a good image. When I had a 60D, I was comfortable shooting with ISO speed 1600. Yes, there was a bit of noise as a result, mostly in the darker areas, but I easily got it cleaned it up with little trouble during post processing. 2400 was also workable, and 3200 if I was really in a jam and needed to get something, even if I couldn't fix all the noise. Indoors with available light and your camera and lens, you'll be forced to make some compromises. You'll have to ask yourself what am I willing to sacrifice a bit to get the image? Slowing down the shutter speed will result in blurred photos. However, if you're willing to trash 25 images of the same subject to get one keeper, then shoot at 1/20th (yes, one twentieth!) or even 1/10th!. In 25 shots or so, there'll be at least one or two that won't be blurred. That's why my smallest memory card these days is 16gb...lots of room to take photos nobody else will ever see. Shooting a group of people, you will likely need to reduce the aperture to f5 or f6 to get them all in focus (Depth of Field). Doing that lets in less light, so you'll have to compensate with slower shutter speed and/or faster ISO speed and deal with the results. Lastly, if you have a filter of any kind on the lens, take it off. The only filters most photographers ever use is a circular polarizer and various neutral density filters...both inappropriate for most indoor shooting. "Protection" filters will almost always cause some image blurring and often end up causing more damage if the front of the lens is hit than if it wasn't on in the first place.