Abigail is protrayed as a clear villain. She too is human like the others. To what extent can you identify with her motives and feelings?

Portraying Abigail as just purely a villain with sinister purposes does not do the character justice.  Abigail is a damaged soul, she is a victim.  As the story goes, Abigail saw her parents brutally murdered by savage Indians while they slept.  Their heads were crushed, while Abigail slept next to them.   Therefore, psychologically, it is easy to see why she is unstable.

Abigail is also a young girl who has been plunged into a new life with her uncle Reverend Parris, a strict preacher, who has put her to work in the household.  Unmarried Puritan girls work in other households, so Abigail gets a job working for the Proctors, where she becomes romantically involved with John Proctor.  I think that she falls for John Proctor because she longs for a strong man in her life.  Her uncle, Reverend Parris is a wishy-washy kind of man.  He is more interested in his career than his family.

Abigail, in my view, clings to Proctor, a strong, manly man who she sees as both protector and hero.  When she is fired by Elizabeth, she is crushed.  Her life is returned to the boring existence of the Parris household, like other young people who engage in illicit behavior, Abigail dreams of getting John Proctor back into her life.

Conveniently, the witch trials, accusations provide her with a method to achieve her goal. I understand Abigail's motives, she wants John Proctor for herself, and needs to get rid of Elizabeth.  It is obvious that she decides to use the witch trials to achieve this end.