• If the word ends in a vowel, or n, or s, stress the last syllable.
• Otherwise stress the second to last syllable.
• If the word has an accent, disregard the first two rules and stress the syllable with the accent mark.

Followup:

1. The accent mark on words like varón and león is to override the "n/s" rule.

2. All the words end in a vowel, and thus the second to last syllable is stressed. I don't have a percentage to quote, but I noticed while looking through the dictionary, that many nouns ended in vowels. The same is true for most adjectives and adverbs.

3. All the words end in an n or an s so the second to last syllable is stressed. All the examples shown are verb forms. Later when we look at verb conjugations we will see that the placement of the stress on the second syllable makes these verbs fit the pattern of the other verbs in the conjugation group.

4. All the words end in a consonant and and thus the last syllable is stressed. Some nouns were found that ended in consonance. Three of the words listed in the fourth column are the infinitive form of a verb. All verb infinitives place the stress on the last syllable.