Examine your list of observations from the event or place you attended. Write down all your discoveries. Summarize all your discoveries together in one sentence in the present tense. This is your thesis.
Begin your first paragraph by explaining where you were and what you saw. Take a couple sentences to describe and explain your reactions to these facts at the time. It's important to constantly write an observation paper with a strong attention to details. The reader should be able to easily picture what you're writing about. State your thesis in the final sentence of your first paragraph.
State one of your discoveries in the first sentence of your second paragraph. Explain what observations led you to that discovery, again providing keen attention to the details. Address the hypothetical argument of someone who might disagree and explain why your discovery is correct. Repeat this process for each discovery, making each one a separate paragraph. Continually search for precise language to keep your points and descriptions lucid.
Restate your thesis in a new way at the beginning of your final paragraph. Summarize your discoveries, using different vocabulary so it isn't repetitive. If possible, end with an applicable quote by a renowned thinker on the subject of your observation.