If you look at the first Gothic novel, The Castle of Otranto,
"The first gothic novel is identifiable with a precision unusual in genre study. Horace Walpole began writing The Castle of Otranto in June, 1764, finished it in August, 1764, and published it in an edition of five hundred copies on Christmas Eve, 1764."
as archetype for this genre, then the following characteristics or elements define a Gothic novel.
The setting is important, usually a scarey place, like a castle or large creepy estate, like in Jane Eyre, where there are lots of doors that lead to secret rooms, locked passageways, unknown elements that exist beyond the doors create mystery and suspense.
There is a secret or a legend that binds the characters behavior. There is a suspected curse that lingers in the halls of the domain that influences the behavior of the characters. The characters experience evidence of the supernatural, either in dreams, visions or through nightly visitations of shadowy figures who look like ghosts but are really people who in the light of day are kept hidden or locked up.
In these novels there is a sense of danger which causes heightened emotions, fear, passion, anger or panic.
The setting includes dark gloomy environment.
"most Gothic novels produce gloomy, haggard settings adorned with decaying mansions and ghostly, supernatural spirits."
The characters usually include women who are in danger or held captive in some way by a forceful male character who dominates the plot.
Think of the novel Dracula, where the figure of the vampire dominates and enslaves women.
"Gothic novels generally focus on mystery and horror, and they usually have some supernatural elements. In Dracula, the supernatural elements are many, starting with the use of a vampire as the title character."http://www.enotes.com/dracula/style
Gothic literature has some element of horror in it, something terrifying, spooky, or horrific. It also often has mysterious elements, sometimes supernatural or dream-like qualities. These stories often take place in a spooky, dark, confined space like an ancient castle or empty manor house, a crypt, or a damp cellar. The themes of guilt and sin repeatedly appear in gothic literature, usually in reference to some crime committed or secrets kept.
Popular gothic authors include Edgar Allan Poe, Charles Brockden Brown, Mary Shelley, Ann Radcliffe, and William Beckford.
The genre of Gothic is a loved and critically acclaimed method for works of popularity. Gothic fiction tries to create terror and suspense and is usually set in isolated old houses, castles, or monasteries, populated by mysterious individuals.
Typical Gothic devices include locked rooms, ancient servants, dusty chambers, and decayed mansions—all properties found in "Frankenstein", "Dracula", and short stories such as “A Rose for Emily.”
Usually taking place in interior spaces of sinister buildings, Gothic fiction also thrives on cultivating an oppressively claustrophobic atmosphere of disturbing mystery and implicit evil. The above mentioned stories provide a good introduction to the genre for students, and they demonstrate how powerfully genre can shape an author’s work.
I would say a principal element is a sense of the weight of the past: hence the heavy, dark, brooding atmosphere; and the importance of the edifice.
Poe was innovative in forming a direct parallel between the edifice and the psychological state of the owner - most obviously in 'The Fall of the House of Usher'; and perhaps also, and more subtly, in 'The Cask of Amontillado'.