Observe the touch, smell, taste, sound and sight of the object without defining what the object is. Sensation merely means to receive the input of environmental stimuli through one of the five main senses. When you receive information on the size and color of an object, rather than the function of an object, you are sensing it as opposed to perceiving it.
Relate the sensed information in terms of previously learned information. Psychologists refer to this as "top-down processing." This occurs when we compare what we sense to what we have earlier experienced. For example, recognizing a furry animal with four legs as a dog is a perception, whereas merely seeing colors and feeling warmth would be a sensation.
Determine the amount of processing that takes place. Sensation happens instantly with little to no effort. You can smell a garden much quicker than you can perceive the type of plants in the garden. Similarly, you must see a flower before you perceive it as a certain type of flower, because perception takes longer than sensation and requires more organization and analysis.
Decide whether you focus on the features of the object or the object as a whole. For example, if you see a bunch of squiggles as nothing more than a combination of curves and slanted markings, then you are most likely sensing the object. However, if you recognize the scribbles as manuscript or a form of handwriting, then you perceive it. The difference lies in the level to which you process the information.