Your social media can stop you from getting a job if there is something that the companies don't like.
A too-long or too-short cover letter may become a hurdle in getting you a job. A good letter may increase the chances.
A not well defined resume, will be not suitable if you want to grab that job. Be sure to provide all information about yourself and previous roles in the resume.
If while giving interviews and meeting with interviewers, you don't have confidence, then you will not get that job easily.
If you are underqualified or overqualified, you will not get the job, because companies avoid such people.
If you are not talking about work with interviewer and rather are badmouthing about former company or boss, then you will not land that job.
Too high salary expectations are not good for getting the job you want. Surely your salary should be decent but don't ask for too high amounts.
If an interview is bad, then it is a sure-shot sign that you will not get the job because the interview is crucial & you can't bombed that.