For best results add an appropriate solvent to the surface being cleaned (glass cleaner for glass, etc.). Wipe the blade clean at every pass to reduce the number of contaminants collecting on the blade (just as you would with a squeegee). Use the blade holder of your choice to obtain a comfortable grip while holding a low angle at the blade tip. This will provide better leverage. Be sure to replace blades often enough to reduce the risk of scratching after working on crusty dirt or sand particles. Remember, the blade is designed to fail against the contaminants rather than pushing them into your surface material.
Scraperite - General Use Plastic Razor Blades with Holder, 5