There are no simple clues for the novice as to whether a vowel is long or short . It simply has to be memorized. However, with practice, this too becomes easy over time and a certain intuitive pattern will emerge as one's vocabulary expands. A good Latin dictionary that marks long and short vowels will make life much easier. It is recommended that the novice look up unfamiliar words to ensure correct pronunciation.
Every Latin word has as many syllables as it does vowels or diphthongs.
Unlike English, which has silent letters, in Latin each consonant, vowel and diphthong is pronounced separately. The rule for where the accent or stress in a Latin word goes is also straight forward. If the word has only two syllables, the accent always falls on the first syllable. If the word has three or more syllables, then where the stress is applied depends upon whether the syllable second to the last has a long vowel or not. If the second to last syllable has a long vowel in it, then the accent is placed on that syllable.