There are two very simple rules about word stress:

1. One word has only one stress. (One word cannot have two stresses. If you hear two stresses, you hear two words. Two stresses cannot be one word. It is true that there can be a "secondary" stress in some words. But a secondary stress is much smaller than the main [primary] stress, and is only used in long words.)
2. We can only stress vowels, not consonants.

Here are some more, rather complicated, rules that can help you understand where to put the stress. But do not rely on them too much, because there are many exceptions. It is better to try to "feel" the music of the language and to add the stress naturally.