When considering a topic for the cause/effect essay, think in terms of a time line. From a fixed point, you will either work backward--looking for and proving causes, or you will work forward--looking for and proving effects.

Be sure the links between them are clear, and remember to find all the major causes/effects. Also be sure to completely understand your topic so you don't miss any secondary causes or effects.

The development of the essay could go one of three ways: either write about the causes of one effect, the effects of one cause or develop a chain of events in which the effect of one cause in turn becomes the cause of another effect, and so on.

The logical fallacy that you should be the most concerned about when developing this type of essay is the Post Hoc fallacy.

This could also be called the "Superstition" fallacy. It is the assumption that just because something happened next, it therefore happened because of what came before.
Superstitions fit this fallacy--just because a black cat walked in front of me this morning, I am doomed to have bad luck the rest of the day.