Keep fettuccine from sticking/clumping while cooking?
Simply put, you have to stir them the first three/four minutes of cooking. Be sure to boil them in enough water (at least 1 liter per 100 grams). In addition to that be sure to buy some good quality pasta. From my knowledge pasta tends to stick when the wheat used is of poor quality. A good pasta should not be transparent when seen in direct sunlight, but it should be of a nice pale yellow color and opaque. Good Italian pasta brands that you can find outside of Italy are De Cecco (which I fear might be quite expensive, and probably not so easy to find), or Barilla (easier to find). Both of them has cooking instructions printed on the package. You might want to cook them for 2-3 minutes less than what's printed, then eventually cook them the remaining couple of minutes together with your sauce.