Japanese is such a ridiculously phonetic language that I'd go as far as guessing it is the easiest language to learn to pronounce. Every word can be written in Hiragana or Katakana and a word always sounds exactly what it looks like. Kanji just makes it easier to distinguish words since there are no spaces; every kanji can be written in hiragana and katakana. In other words. the "letter" た is pronounced TA exactly the same way in every word. Most letters have a consonant and vowel sound so you can type them this way too. There are a few ways people write in romaji. A lot of people and textbooks will write Tabeyoo (lets eat) for たべよう. I think this is ridiculous because 1 in the Hiragana, if you go letter by letter, its ta-be-yo-u. （たーべーよーう） 2 You can also hear a slight difference between a word with an "おお” OO ending and an ”おう” OU　ending and 3 If you type this into a keyboard youd have to type tabeyou, not tabeyoo So I recommend using romaji letter by letter since Japanese is extremely phonetic. The only time it is not phonetic is the "wa" "o" and "e" particles which are actually using the letters for "ha" "wo" and "he" and .....I forget the word for it but the chopping off of certain sounds (desu actually sounds like des and ashita actually sounds like ashta, but these are always romanized as desu and ashita). Apparently there are 2 tones which makes it really hard to not have ANY accent but these tones are VERY subtle, only occur in a few words and are not romanized so you're better off not to worry about it til you have your basics down. I'm sorry this was a little roundabout.

You might want to practice double consonants, like in kitte, きって. It's different from kite きて in that it has a small っ. This っis a silent pause, lasting for the same length as an individual syllable. "ki -- te". Many words have this "double consonant", and it's probably very hard to understand what you're saying if you don't pronounce it correctly. Of course double vowels are as important. Ou is pronounced almost like oo, so you don't shift from o to u. Ei sometimes doesn't shift from e to i, and becomes "ee". I'm not really sure why though. You can listen to the examples on http://www.saiga-jp.com/kanji_dictionary.html and practice.

It's almost accurate what ZZZ said (he's really good). Just add slight details. 1. There are some textbooks mention that, when 'i' or 'u' is placed between voiceless consonants as 'k, s, t, p, h', we usually whisper the verbs. I think it's worth to hear that, we do this really. kitte (stamp), tesuto (test), kuji desu( it's nine o'clock.) We can recognize what you want to say, but if you speak vowels too loud in that phrases, it sounds strange, not natural.(so we can find you are Gaijin...sorry, but it's true!) 2.Some books say there is a little difference when the letter 'n' comes before some specified consonent like 't,d,r'(like n in sun) 'b,m,p'(like m in simple) 'n,k,g'(like ng in king). But actually we Japanese don't recognize the difference! So don't care about it.