There are many different ways to approach an observational study. You can observe natural occurrences, human behaviour, animal behaviour and much more. Start out with a strong plan for your study and a quick hypothesis about what test results you will encounter. Record all your findings to get the most accurate data.
Observing Human Curiosity
People are curious creatures who sometimes feel the need to ignore direct instructions. You can observe this by setting up a "disguised observation study." This means that test subjects will not know that you are observing their behaviour. Set up a wood box large enough to stand in somewhere in public. Drill a 1-inch wide hole into the box at eye level when you sit down. Place a sign outside the box that says, "Do not peek." Have another person stand outside the box to observe how many onlookers pass by the box without peeking. Sit inside the box and count the number of people who stop and peek. They will have to noticeably bend to peek inside, so there can be no mistake they were looking). Based on the data you collect, you can create a report on whether the majority of people in your community would disobey a direct order to satisfy their curiosity.
People act in interesting ways when confronted with an attractive member of the opposite sex. A singles bar is one place to observe such interesting behaviour. Record the different behaviours exhibited by both men and women by setting up two decoys in a singles bar. Choose one attractive man and one attractive woman to sit alone, separately, at a bar. Stand aside and observe the people who approach them (the people who approach should not know you are watching). Record which decoy got the most attention and create a hypothesis about why you think one decoy was more popular than the other.
Insect Food Preferences
Choose an insect you commonly see outdoors, such as ants. Research the insects to determine what is usually in their diet. Select two different foods they normally eat and prepare a sample of each. Set out the samples near the insects' nest. Sit back and wait to see which food the animal prefers. You can also work with the same food, but choose different preparation methods. For example, you can compare the preference an insect has between an apple grown to sell at a store as opposed to an apple grown naturally in a local garden. Record your findings.
Cold Vs. Hot Hands
Yale University researchers decided to tackle the myth that cold hands indicate a person with a kind demeanour. Study participants answered an assortment of questions while holding a cup of either cold or hot liquid. Participants holding warmer cups were noticeably kinder and more generous than the participants holding cold cups. You can replicate the study to see if the people in your community react the same way to cold and hot. Search for signs of kindness like participants saying "thank you" or answering questions with kind and generous responses. Do not tell the participants about the purpose of the cup or it may alter their answers.