Start a simple sentence. Leave a blank where the subject, or noun, should go. For instance, your simple sentence might be "The (blank) went to the store for some milk."
Fill in the blank with an appropriate word for a subject that is an example of denotation. If you use generic, universal phrases such as "adult male" or "12-year-old girl," then these are examples of denotation. However, if you fill in the blank with a connotative word, such as "dude" or "tween," then these words evoke a particular feeling that will be interpreted by the reader. The word "dude," for instance, might summon the image of a dimwit, while a "tween" might be a pre-teenie bopper who is into a particular music style and looks a certain way.
Use generic and universal words that are defined by everyone similarly. When you create the sentence "The adult male went to the store for some milk," you are stating more fact than feeling, which is the definition of denotation.
Reread your sentences to see whether you use denotation correctly. Ask yourself if your sentence could be interpreted differently by different readers. If the answer is "yes," then your sentence is connotative rather than denotative. Change connotative subjects in your sentences to denotative by taking out the interpretive noun and replacing it with something that is strictly defined.