There are two very simple rules about word stress

Word stress, also called lexical stress, is an important suprasegmental feature in English because it determines so many other aspects of pronunciation

Word Stress

First, word stress determines which vowels in a word will be pronounced with a clear vowel vs. schwa.
Second, word stress impacts the pronunciation of consonants: the unvoiced stop consonants /t/, /p/ and /k/ are pronounced in English with aspiration either initially or in stressed syllables, but without aspiration in non-initial unstressed syllables.
Third, word stress determines which vowel(s) in a word will be pronounced longer vs. shorter, including which vowel gets the primary stress and can therefore be marked with even greater length via focus.
Fourth, word stress determines which syllable is marked with the highest pitch, lowest pitch or some other distinct pitch change.
Finally, word stress also determines which syllable, if any, will be marked via increased volume.

There are two very simple rules about word stress:

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.)

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.

A. Stress on first syllable

ruleexamples

Most 2-syllable nouns

PRESent
EXport
CHIna
TAble

Most 2-syllable adjectives

PRESent
SLENder
CLEVer
HAPpy

B. Stress on last syllable

ruleexamples

Most 2-syllable verbs

preSENT
exPORT
deCIDE
beGIN

Compound words (words with two parts)

ruleexamples

For compound nouns, the stress is on the first part

BLACKbird
GREENhouse

For compound adjectives, the stress is on the second part

bad-TEMpered
old-FASHioned

For compound verbs, the stress is on the second part

underSTAND
overFLOW

When we stress syllables in words, we use a combination of different features. Experiment now with the word 'computer'. Say it out loud. Listen to yourself. The second syllable of the three is stressed. What are you doing so that the listener can hear that stress?

A stressed syllable combines five features:It is l-o-n-g-e-r - com p-u-terIt is LOUDER - comPUTerIt has a change in pitch from the syllables coming before and afterwards. The pitch of a stressed syllable is usually higher.It is said more clearly -The vowel sound is purer. Compare the first and last vowel sounds with the stressed sound.It uses larger facial movements - Look in the mirror when you say the word. Look at your jaw and lips in particular.

A useful thing you can do is to help students see connections with other word families. Patterns can usually be found, for example:

O o final neutral

o O oo finality neutrality

O o o finalise neutralise

o o o O o finalisation neutralisation