When reading Japanese words, it can be helpful to keep the following pronunciation guidelines in mind:

• Japanese vowels by themselves are pronounced like Spanish vowels, so
  a is pronounced like the a in blah
  e is pronounced like the e in hey
  i is pronounced like the ee in week
  o is pronounced like the o in dote
  
• Japanese is not always pronounced the way it is written. Fortunately, since English-speaking audiences read the manga translated, they needn't worry about wa looking like ha or their chans looking like chians. However, one anomaly which frequently is seen by the casual reader is the "ou", like one might see in a popular translation of "Taishirou", "four elders" in the English version of Samurai Deeper Kyo. The fact of the matter is, that "ou" is pronounced like a strong "o", as in "yo", not "u" as in "you". There are many ways to render this strong "o" sound in romanji, the most correct of which is "ō". (An "o" with a macron bar over it.) However, most translators decline to use the ō due to the fact that it is inconvenient. The following are the most popular methods of rendering the "ō" in romanji:
  
  1. "o", just pain old o, which is the easiest for the casual reader to understand. Most commercial translations use this.
  2. "ou", which preserves the original Japanese spelling. This is used by most on-line translations for a number of reasons, one being that for those with some knowledge of Japanese pronunciation can see it and recognize the "strong o" sound, which would be undetectable if rendered only as "o".
  3. "oh", more commonly seen in commercial translations than amateur ones, it's a way to distinguish the "strong o" sound from a normal o in a way that a casual reader can immediately understand.
  4. "ō", as previously addressed, is in fact, the most accurate way to convey the "strong o", but is inconvenient to type, as it requires several keystrokes to produce, as opposed to the one or two required for alternatives.
• Double Japanese vowels, frequently written with a macron bar over them, have extra emphasis on them. The difference between ojiisan and ojisan is the difference between a grandpa and an uncle, and either party could be offended if you addressed them with the incorrect word.
• The most common mistake when pronouncing Japanese has nothing to do with vowels at all, but with stress. This is a problem seen time and time again with dubbed anime that is otherwise flawless. In English, the romance languages, and others, the stress of a word falls on the second to last syllable in almost all cases. Like in "computer", if you say it aloud, you say "com-PU-ter", or in "summer", you say "SU-mer". In Japanese, unless in the case of double vowels, there is no stress. This can be a difficult concept for a western-language speaking person to understand. The best way to figure out how to pronounce a word is to say each syllable separately, then run what you just said together. Examples: many people pronounce "Hiroshima" as "Hiro-SHI-ma", but "Hi-RO-shima" is closer, or "Kagome", which in the dub of Inuyasha is called "Ka-GO-me" is actually pronounced closer to "KA-gome". If you have trouble with saying all of the syllables separately, try putting the stress on the third to last syllable. It's not a perfect method, but it's more accurate than placing the stress on the second to last syllable by leaps and bounds. For instance, in the city "Kawanakajima", if that seems too much, "KawanaKAjima" is better than "KawanakaJIma".