Only if your monitor's "auto-adjust/auto-config" function is clearly malfunctioning, proceed to attempt manual configuration using this guide. My new [Aug 2010] el-cheapo LCD monitor —and I assume almost all other recent monitors— auto configs "clock/pitch" and "phase/focus" both much more accurately and much faster than I could possibly do it; manual override attempts would just mess it up.
Use of this image assumes an exact one-to-one mapping between the computer's logical pixels and the display's physical pixels, which for newer displays is probably not true (or only true at lower resolutions such as 1024x768). If this displays either a regular two-dimensional pattern of uniform bright spots or a uniform pattern of pencil-thin stripes alternating light and dark, it is signaling its uselessness.
If you do anything manual at all, first try changing just the refresh rate (e.g. 60/70/72/75Hz) on your PC.
Image should show a steady and bright (extremely small) checkerboard pattern. On LCD monitors connected via analog connection (do not try to adjust monitors connected via digital connection to this test pattern), use monitor's auto-adjust/auto-config or manual clock/pitch and phase/focus controls, if necessary, to eliminate broad vertical banding (clock/pitch), and shimmering horizontal streaking (phase/focus).
After shimmering horizontal streaking is eliminated, further adjust phase/focus to make checkerboard pattern as crisp as possible. (Some settings of phase/focus may make the checkerboard pattern so un-crisp it becomes a uniform gray and essentially disappears. This can also occur if brightness/contrast are set way high; in this case turn brightness/contrast down temporarily, adjust for this test pattern, then turn brightness/contrast back up.)
If no clock/phase combinations are very satisfactory, try selecting a different refresh rate (e.g. 60/70/72/75Hz) on your PC.