Know the reason
If your parents are disapproving of a person you are dating, you need to know the reason. Try to be honest with them and ask them the reasons for their decision in a calm situation. If you can change the things that they are concerned about, tell them to the person you are dating. In this way, you can also get to know about any misunderstandings your parents might have.
Try to convince
If the reasons that your parents gave can be sorted, try and convince them. You can come up with good things about the person you are dating and give reasons of why you like him or her.
If you are not able to convince parents on changing the decision, find some support within the family. You can talk to your aunts or elder brothers or sisters for that matter. Try to find someone who can influence your parents on making the decision in your favour.
Do not take emotional decisions
Always remember that the parents might have a point. You should not be taking any decisions emotionally or just to prove your point. This can change your life in a bad way so always keep your elders in the loop so that they think what you are up to.
Give the relationship some time
It is always good to give the relationship some time to develop. You know the person you like over a certain period of time so do not take any hurried decisions.