As per z1ppy,
Calculate one litre of water to every 125g of dried pasta. Bring the water to the boil; add a teaspoon of salt for every two litres of water and add the pasta. After it comes back to the boil let it continue boiling for three minutes. Turn off the heat, cover the saucepan with a towel and the lid, leave it for 5-8 minutes according to the thickness of the pasta, eg five minutes for spaghettini, eight for maccheroni rigati, which are short tubes, ridged and thick. At the end of this time the pasta should be just al dente.
The addition of a big lump of butter left to melt on the top of the pasta as it is served, or of a little olive oil put into the heated dish before the cooked pasta is turned into it, are both great improvements.