To make Paella: What is best practice to cook the rice?
Best practice: You fry the vegetables and the meats. You 'fry' the rice in oil (extra virgin olive, of course). Just make sure all the grains are covered with oil (don't deep fry) Then you add a hot broth. Leave it on a nice flame for about 10 min. Put in a hot oven for the remaining 10 min. Done.
Best practice: The paella (the pan) should not be crowded with rice. Too much rice will not give a good result.
Paella with onion is not paella (don't ask me why, as peppers can be added). In theory, onions will add moist to the rice and will make it 'pass' it's point.
The rice should be 'al dente' done but not overdone.
Leave the paella in peace for about 5 min, covered with a newspaper.
For the special ingredient, look at my answer to this question.
There are several cooking recipes on wikipedia, for starters.