Unless you're being asked to do some research as part of your compare/contrast project, make sure that you choose 2 things that you feel comfortable discussing, at length.
If you want to write a successful compare/contrast essay, you'll need to avoid writing about really obvious differences and similarities. For example:
How to Prepare for the Compare/Contrast Essay | …
As the term implies, compare and contrast transition words are transitional phrases/words that show comparison and contrasting relation of two ideas. They are also used to emphasize negative and positive ideas. For you to have a clue on what exactly are they, here is a list of the most common contrast and compare transition words and phrases that are used in everyday writing and speech.