Spanish rice varies greatly depending on the cook. I change mine around depending on ingredients I have on hand. In general, the main ingredients are as follows.

Using 2 Tablespoons of oil, stir fry until lightly toasted:

1 cup of uncooked white rice

add and sauté a bit longer:
1 diced medium onion
¼ cup of diced mild green chilies, such as anaheim or poblano or even green bell pepper

Add 2 and 1/4 cups of chicken broth (you can substitute 1 chicken bullion cube dissolved in 2 1/4 cups of water)
¼ cup tomato sauce
½ cup canned diced tomatoes with juice
½ tsp red chili powder
1 minced garlic clove

Cook covered over low heat until liquid is absorbed. I use a skillet and it takes about thirty minutes. If you use a rice cooker, it burns on the bottom because the rice cooker tends to burn the tomato sauce.

Vary the spices to your taste. My mother doesn’t bother to stir fry the rice ahead of time and it turns out just fine, but if you wonder why it doesn’t taste like restaurant Spanish rice, it is likely the toasting. Toasting imparts an almost nutty flavor to the rice. When toasting (sautéing in oil or vegetable oil) let the white rice uniformly change color to a dark brown. This means that you must stir it almost constantly while browning.

For a slightly different taste, mince 1 to 2 tsp of cilantro and add when you turn off the rice. Let it sit covered for at least 5 minutes and then stir in. It will steam slightly and infuse the rice with a citris flavor.