You should consider developing your paragraph by comparison and contrast when you are describing two or more things which have something, but not everything, in common. You may choose to compare either point by point (X is big, Y is little; X and Y are both purple.) or subject by subject (X is big and purple; Y is small and purple.). Consider, for example, the following paragraph:

Although the interpretation of traffic signals may seem highly standardized, close observation reveals regional variations across this country, distinguishing the East Coast from Central Canada and the West as surely as dominant dialects or political inclinations. In Montreal, a flashing red traffic light instructs drivers to careen even more wildly through intersections heavily populated with pedestrians and oncoming vehicles. In startling contrast, an amber light in Calgary warns drivers to scream to a halt on the off chance that there might be a pedestrian within 500 meters who might consider crossing at some unspecified time within the current day. In my home town in New Brunswick, finally, traffic lights (along with painted lines and posted speed limits) do not apply to tractors, all terrain vehicles, or pickup trucks, which together account for most vehicles on the road. In fact, were any observant Canadian dropped from an alien space vessel at an unspecified intersection anywhere in this vast land, he or she could almost certainly orient him-or-herself according to the surrounding traffic patterns.