You need to use a tactful approach. Since you already know the person is shy and not very social, be extra careful and cautious in trying to make them feel at ease. Make them comfortable from the start so that they start opening up. Keep a slow pace and introduce yourself, but do not be disheartened if the response is not how you expected. After telling your name, make light conversation. Do not stay there for too long as it will intimidate the person and make them uneasy. This is a good way to make a decent first impression.
After the introduction is done, it is essential that the contact doesn’t break for too long. Some space should be given but try to connect again after some time so that you stay in his/her mind. If you bump into each other on a party, make some casual conversation like, “did you taste the appetizer, it’s really good”. It is a very simple conversation starter and can keep the chat going on. If you are in school together, take a seat near him/her so that there are more chances of an interaction. This will help them in opening up to you. You should also compliment them once in a while but keep it subtle.
The golden rule in such scenarios is never to put pressure on the other person. It is human nature that if you like someone and are interested in them, you might feel inclined to rush things. While you may be thinking it’s going real slow but for the shy person it’s the perfect pace. If you try to take things fast, they will turn away. Remember that it will take some time to develop an equation and gain trust. Once you gain his/her confidence, they will be comfortable with you and you will get a chance to ask them to be your valentine.