Here are some things I discovered while using and learning about the Canon XSi/450D. One of the most important things to learn, particularly for a new DSLR user, is to become very familiar with the lenses you use and get to know their “sweet spots.” I share more about my experiences with lenses elsewhere in this blog.

• Image sharpness - using a small aperture, will help increase sharpness and depth of field in a photo. Each lens has a different “sweet spot,” f-stops usually found in the mid-range that produce the sharpest images.
• Custom white balance - Use a custom white balance to obtain more natural looking colors when taking photos inside. It is very easy to set with the XSi [manual page 90].
• High ISO - To get the best possible results when shooting at high ISO settings, expose well and avoid underexposure. This is true for any camera, not only the XSi.
• Simulate ISO 3200 -  switch the camera to ISO 1600. Set Exposure Compensation to -1. As a safety net, shoot RAW so you can make necessary adjusts when editing.
• Continuous shooting does not work when High ISO Speed Noise Reduction is enabled.
• When AF Lock is enabled, the XSi won’t focus automatically when you half-press the shutter release button. You must press the (*) button to focus.
• Increased noise - when using Highlight Tone Priority mode, there will be an increase in noise in dark areas. The problem is worse when using HTP to photograph high contrast scenes.
• Format memory card - to keep your memory card so it provides optimal performance, do a low level format on a regular basis. I generally do a low level format once a month.