Theres a few key factors that have worked for me.
Actually be deserving. Sounds dumb, but alot of people just expect pay increases regardless of their attendance, performance, ect.
Never straight up ask for a pay increase. Ask for a performance review. At the end of the review, ask if you are eligible for a pay increase. If not, ask what you can do to change that.
Ask them in an appropriate setting. For example, if you work retail, don't walk up to your manager on the floor while rubbing your fingers in a "money" gesture. Wait until your boss is not busy, then ask to speak in private.
Be understanding! Even if they say yes, it's probably not going to happen immediately. Don't get discouraged or gripe about it with co-workers, because trust me on this- everything said gets back to the boss eventually.