Note: Native Resolution
LCD monitors, including laptop screens, typically run best at their native resolution. You don't have to set your monitor to run at this resolution, but it's usually recommended in order to ensure you see the sharpest text and images possible. LCD monitors generally come in two shapes: a standard proportion of width to height of 4:3, or a widescreen ratio of 16:9 or 16:10. A widescreen monitor has both a wider shape and resolution than a standard ratio monitor.
If you're unsure of your monitor's native resolution, check the product manual or go to the manufacturer's website. Here are typical resolutions for some popular screen sizes:
19-inch screen (standard ratio): 1280 x 1024 pixels
20-inch screen (standard ratio): 1600 x 1200 pixels
22-inch screen (widescreen): 1680 x 1050 pixels
24-inch screen (widescreen): 1900 x 1200 pixels