Quitting a job is never easy. Suppose you are tired of a job and feel like you are not valued even with giving it your all. That means it is time to go but do not make rash decisions but take your time. Look for opportunities within the company or elsewhere first. Make sure you are not bad-mouthing your current job! When you bad mouth a company/position, hiring managers/supervisors feel like you can do that to the job you are applying to. Do not say you feel down and not valued. Most of the time, hiring managers/supervisors take that as maybe you are just playing the victim. Look for another job and get hired and make sure while getting hired, give a two-week margin so you can provide a two-week notice. Also, if you are in management, make sure you give a month's notice.