Use the Tax Withholding Estimator on the IRS web site to figure out what to put on your W-4 form.
But who is going to claim you as a dependent? You didn't give any information about your living situation. Are you married? If so, your spouse cannot claim you as a dependent, and probably no one else can, either. If you are not married, it's unlikely that anyone can legitimately claim you as a dependent if you are working, even if they provide a large portion of your support.
Try using the tool at the following link on the IRS web site. Pretend that you are the person who wants to claim you as a dependent, and see if it says they can claim you.