If you're a high school or college student who is taking Spanish right now and are struggling with pronunciation, this article will give you some practical advice and hints about how to improve your pronunciation.
The most important thing you can do is to listen with your full attention to the sounds of Spanish, as spoken by someone who speaks it well. Remember, some native speakers of English would not be good models for teaching a foreigner, so choose your model carefully. I often recommend that students listen to songs, get the lyrics and sing along -- karaoke style. One website in particular has lyrics and video, and although often I find grammatical or spelling errors, I still recommend it. I also recommend one musical video in particular by Shakira -- not only because is it very artistic, but because the close ups of her face make it possible to see how she pronounces many sounds. This may sound silly, but babies watch mouths when they are learning to speak.
Next, pay close attention to vowels. For practical purposes, Spanish has five -- and they are all pure. It may seem like a simple thing, but English speakers have to reign in the range of vowels in order not to have a bad accent. Here are some clear guidelines, based on the "standard" American pronunciation of the English words in these examples:
The letter A is pronounced as the A in the English word father, never as the A in cat.
The letter E is pronounced almost* like the A in the English word paper, never as the E in meet.
The letter I is pronounced like the EE in the English word meet, never as the I in imitate.
The letter O is prononced almost* like the O in the English word hope, never as the O in office.
The letter U is pronounced like the OO in moon, never as the U in up.
* Avoid the upglide into a final Y (as in they) or final U sound (as in how) in these two English examples.
Finally, Spanish consonants present English speakers with some subtle, but important, problems. The most obvious is the way English speakers tend to explode the consonants P, T and K sounds (the latter being found in que, qui, ca, co and cu).
Practice saying the words Pepe, Carlos and Tomás with your hand an inch in front of your mouth. If you feel air, you're exploding the consonants too much. These sounds should be reigned in, so to speak, so as to tend to sound a bit more like B, D and G, respectively.
The trilled R causes a lot of English speakers trouble. There is a way to trick one's tongue into saying it! First, you have to be aware that when pronouncing even the simple R sound in Spanish, the tongue is not positioned in the same place as in the English name Ralph. It is positioned in the same place as when pronouncing the tt or dd in the English words palmetto or paddle or rattle. Once you figure that out, place a D in between the words EL REY > EL DREY and try practicing that. It will probably take a few tries, but you'll actually feel the difference when it happens.
Lastly, when a word ends in a consonant and the next in a vowel, the consonant "goes over" to the vowel when speaking. Likewise, if one word ends in a vowel and the next begins with one, they will also elide into one syllable, more often than not.
Don't forget: there is no substitute for consistent practice accompanied by attentive listening. Don't give up.
Oh, and you might enjoy this website too, for practice with some poetry in Castillian. Both sound and text may be found here.