As from drama, Gothic literature emphasizes on emotion and reflects on a sense of drama, this could be kidnapping, blackmailing, murdering or people going mad/dying because of their (mental) illness.
Obviously it aims to explore a darker and more tragic theme than the Romantic works of that period.
During the first few years when Gothic literature just appeared, the writers followed a model that the background will always be in an old castle, an abandoned height or somewhere forsaken.
The atmosphere would always be mystic and dread, emotions running high, with a plot of, generally, hidden secrets, ghost, vampire and miserable life.
Protagonists in Gothic literature often have strong mind, even being isolated or alone.
This isolation can be either mentally (cut off from people around) or physically(trapped in a coffin alive).
Another main characteristics of Gothic literature which would be easier to define is the "Damsel in Distress" setting, either this "damsel" being threatened by a man or just the circumstance that they find themselves in.