How do I know which syllable I need to emphasise in a Spanish word?

In Spanish, every word has one syllable which is emphasised (or stressed) more than the others. Pronouncing single syllable words like yo, nos, ir, ver etc should be no problem, but what about words with more than one syllable? If a word has an accent (á,é,í,ó,ú), then this is the syllable which is emphasised. This is especially important when it comes to distinguishing between tenses- for example amo, (emphasis on the first syllable), which meaning 'I love' verses, amó (emphasis on the last syllable) which means he/she/it lovedFor words without an accent, there are two rules to follow:if the word ends in a vowel, an n or an s, then the penultimate (second to last syllable) is emphasised perro, piscina, desafortunadamenteif the word ends in a constant (that isn't n or s) then the last syllable is emphasised tener, nosotros, escritor