|When should Spanish "h" be pronounced?|
The answer is: Never!
A lot of Spanish students know this, they know the "theory", but when putting it into practice, they still need to be very careful, as sometimes, they still pronounce it. We must understand English "h" has a different treatment, so in case you are an English speaker, you'll need to be careful about this.
Don't worry, it is just a question of practice. The more you listen to Spanish songs, radio stations, tv movies or Spanish DVD's, the more you will be get used to the pronounciation of this letter, or better said, to the non-pronunciation of this letter!
Hope this helps!