First of all, it is best to repeat that spaghetti should be eaten exclusively with a fork, without help from either a knife or a spoon (which should be used only for soups).

When you eat spaghetti, your fork should be slightly tilted toward the plate, not held vertically. Just pick up a few strands of spaghetti at a time (about 2-3), twirl them clockwise, and bring a neat bundle to your mouth, trying to avoid any dangling strands if possible.
source:www.accademiaitalianagalateo.it

This is the technique most Italians use, but if we want to talk about good manners again there are other rules you might be interested in below.

5 etiquette rules for eating spaghetti.

1. Never help yourself with your hands

Eating with your hands is a typical practice in cultures such as India, in which case it would be absolutely correct not to use cutlery. For us Italians, however, it is different, especially with spaghetti. It is absolutely forbidden to use your hands to eat it. Read here to find out what we eat with our hands here in Italy.

2. Hold your head high

Fear of getting dirty often provokes eating hunched over the plate. It is best to avoid bringing our faces close to the plate of spaghetti! It is always only the fork that approaches the mouth and not vice versa.

3. The spoon is only for soups

Forbid using the spoon in an attempt to form a perfect twirl of spaghetti. A good rule would have the fork, tilted and never vertical to the plate, intercept 2 or 3 spaghetti and then roll them clockwise to form a perfect skein to bring to the mouth.

4. Cut the Spaghetti? Only in this case.

There is only one possibility in which it is acceptable to cut spaghetti: if the person eating it is a boy or girl who has not yet perfectly mastered the fork. Sorry to disappoint you, but above the age of 4 or 5 it is no longer allowed!

5. Do not serve them on a flat plate

Remember that spaghetti is the first course in Italy, which is why it is almost always served on bowl plates, never on a flat plate. In addition, a bowl is also useful for containing spaghetti and keeping the sauce concentrated on them.