Make an observation. To form a hypothesis, notice something and watch what happens. For example, you might observe that you sneeze and cough.
Ask a question about your observation. If you sneeze and cough, then your question may be, "Why am I sneezing and coughing?"
List potential causes of what you observed. In the case of sneezing and coughing, you might list catching a cold, catching the flu or allergies as potential causes of your symptoms.
Form a general hypothesis. A general hypothesis is not a testable hypothesis, but it is an educated guess based on your previous experience, knowledge or research. In the case of sneezing and coughing, your general hypothesis might be: "Sickness and allergies cause coughing and sneezing." That is a basic idea about the potential causes, but it is not specific enough to test in an experiment.
Refine your general hypothesis by giving it a direction. For example, your refined general hypothesis may be: "I have allergies in spring." The refinement gives a general direction based on the time of year and it offers a potential cause, but it is not testable.
Write your testable hypothesis. The testable hypothesis must answer the question you asked previously by proposing a cause of the observation and giving you something to examine. For example, your hypothesis about why you sneeze and cough might be: "I sneeze and cough in the spring because I have allergies to plant pollen." This testable hypothesis states the observed problem and gives you something to examine as a potential cause. Then you can create an experiment to test your hypothesis. An example is to undergo an allergy test to learn whether or not you are allergic to plant pollen.