they are certain rules and exceptions to stressing a word. you need to first of all be able to differentiate between nouns, verb, adjectives, compound words etc. with the knowledge of this, you can easily  place the stress on the right syllable. 

perfect is stressed as PERfect. 

include is stressed as inCLUDE

interest is stressed as inTErest

employ is stressed at the second syllable as emPLOY

Therefore, perfect has the same word stress as cement on the first syllable.

NOTE; generally speaking words beginning with ‘un’ or ‘in’ have the stress on the second syllable.