Legal immigration from Spain

Where can I get information about a Spanish citizen immigrating to the U.S. legally? Is it just a matter of not exceeding a quota, or are there other considerations (employment, marriage, etc.)?

www.uscis.gov would be your best place to start

Basically, you aren’t immigrating unless:

  1. you have a job here and your employer is willing to sponsor you
  2. you have a relative who will sponsor you
  3. you win the diversity lottery
  4. you are a refugee/asylee/etc.

there are no visa quotas that I am aware of that applies to Spanish citizens.
Unless you have a job or a relative, really your only choice is to win the diversity lottery.