The first and the foremost thing you can do is to change your shoes and switch to flat ones. Try avoiding heels whether it is an inch longer, it will also effect. Do not wear pumps ballerina shoes for your entire life, but if you start searching you will definitely find variety of shoes which are flat and they can be worn with formal dress as well as semi-formal attire, besides casual.
If you are standing among a group of people try standing at such position where you will look short as compared to other. If the gathering is on the stairs stand at the bottom, or you can lean at a supportive stand or an item.
You can also stand among people who are taller than you, so that the environment gets neutralized for you.
Your wardrobe also plays an important role in making your look taller or shorter. Try wearing clothes which will help you in portraying a short height look. Try choosing clothes like short skirts, dresses which have horizontal lines instead of vertical and avoid long gowns at parties with flowing veil. Try buying short jackets instead of long ones, and clothes with dark hues.