If you want to write a successful compare/contrast essay, you'll need to avoid writing about really obvious differences and similarities.
For example: Tell us something we don't know (or might not notice)!
You can't write a good compare and contrast essay without first reading what you've been assigned!
Moreover, to generate a good essay you've got to read them carefully.
Depending on how organized your thoughts are, you might just jot out a few main ideas on a blank sheet of paper/computer screen or you might actually want to make up an actual list with columns for things the texts share and things they don't.
During this phase, just write down whatever comes to mind, no matter how miniscule you think it may be.
Finally, you'll add a concluding paragraph that sums up your argument and restates, perhaps in a new way, why you feel that what you talked about is important both to your texts and to the world at large.
Once you've got your outline set, writing the essay mostly becomes a matter of supporting your points with evidence from the works you read.
Once you've read everything you have to, draw up lists of how those works are similar and different to each other.
This is when those notes you might've taken back in step one could come in handy.