First of all you need to pick up two works of literature including a comedy and a tragedy. It is up to you whether you select classic literature or the modern one because there is no major difference between classic and modern literature regarding the basic elements of comedy and tragedy.
Now, you should read both works very carefully and keep on writing down major points or aspects that you find along with way.
Your notes should contain the basic points of characters, story, plot, timings and settings of both works which will help you to make a good comparison of both works.
You need to make corresponding notes by following the plot, story, characters and settings. Draw a vertical column for writing down your notes in an organized way which will help you to identify the most prominent elements of a tragedy and comedy.
Now, carefully compile a list of contrasting elements of both works which will help you to get a better understanding of the differences between two forms.
Usually a tragedy creates a huge impact on people all over the world but a comedy has a little impact. A tragic hero normally falls because of a single mistake which is usually an error of judgment while the hero of a comedy can have many flaws and commits many errors.
Another important element of a comedy is that it makes the reader or audience feel superior over grievances but a tragedy always highlights the limitations of people.
Another important element between a comedy and tragedy is that the characters of a comedy are ordinary or common people just like us but the tragic characters are extraordinary and they entertain a greater impact on the audience.
Comedies are usually drawn in real world in which people can identify them with the characters easily. However, tragedies always show a strong war between evil and good and the acts of characters in a tragedy cannot be performed by ordinary people.
A tragedy always ends up unhappily where the hero usually makes sacrifice for greater good but in a comedy, the ending is always happy and you can witness it in the romantic comedy of modern literature.