Breathe deeply and clear your mind. If your brain is filled with thoughts about what you're going to eat for dinner or what you're going to wear tomorrow, you'll find yourself staring at your subject without observing at all. Concentrate on concentrating. If you have trouble concentrating, suggest the skill to your subconscious. Say to yourself, "I intend to concentrate on the matter at hand. If my mind wanders, it will automatically correct itself."
Choose aspects that are easy to focus on. Ask yourself, "What do I notice? What's different since the last time I looked?" Pay attention to color, shape, size, shadows, shading, movement, speed, duration, intensity. Look at the object of your observation as though you will be expected to describe it to someone else.
Take notes in steady intervals. If you're observing a crowd of people for one hour, intend to take notes every five minutes. Looking back at your notes, you'll see that you have recorded even the most subtle of observations. Remain consistent, so that if you write the observation, "Nothing changed for an hour," you have 12 instances of writing "No change" to back up your claim.
Write your notes in a way you can understand them. If you're using shorthand, coded words or symbols you made up, keep an answer key handy for easy memory. Be as legible as possible. Leave spaces between your notes so you can add observations later. If necessary, neatly rewrite your notes when you have the time; you don't want to look back at them later and wonder what you were trying to convey.
Review your notes right after the observation while the details are fresh in your mind. Add anything you might have forgotten.
Compare notes. If others have the same observations as you, you'll know you are on track. If others have additional or different notes, jot down the discrepancy just in case you missed something.