Analyse the reasons for feeling shy in the first place. For example, you're not confident in your appearance or you feel that you are not as smart as the people around you.
Understand that all people tend to think more about themselves and not about you. Do not take everything personally. If you feel that someone is neglecting you, it is quite possible this person is having a bad day or just does not care.
Prepare for the day ahead. Make a list of questions that you can ask people like current events, the weather, books they have read etc. Remember, most people like to talk rather than listen.
Stay confident. Do not let the panic attacks take over you. Straighten your back, pull your chin forward as this will make your posture more positive. The way you hold yourself and what you say, is how people will perceive you. Tune in advance by doing simple breathing exercises.
If you do not like noisy clubs, public speaking or large companies, there is no reason to force yourself to feel uncomfortable. Find people that you love to walk with in the park, go on a campaign to plant flowers or watching ballet as you spend more time with them. By the way, all those night clubs and noisy parties does not necessarily guarantee a good time.
Be proud of your successes. Analyse your last day and look for moments in which you behave the way you wanted, forgetting about shyness. You can even record your victory in a diary. Keep focus on how you get something and avoid thinking about the situation where you failed.
Try not to over-think everything and take things one step at a time. You do not need to rush into a large gathering and start talking to everyone, just take your time and slowly you can overcome your shyness.