You may think of yourself as the unobservant type - you don't really care how others dress - but you make snap decisions about who to talk to in a crowded party and where to sit in a dimly lit bar. Here are 3 ways to manage how people perceive you in the first 5 seconds.
This is your general shape--do you look like you're slouching or frumpy? If you're clothes are too baggy or if your coat hangs off your shoulders people will think you are small in personality and confidence. Conversely, if you look like you're busting out of your clothes because they are too tight, people will think you are self-absorbed or that your beer gut could use one less draft.
This is the ratio between your torso and your legs. Great cars approach a 50/50 ratio and so do people--you want a good balance in the overall appearance in length. Equalizing both your legs and your torso will make you look more confident and more powerful.
Everyone is different but there are some basic color groups of skin tone and hair. Medium contrast clothing for caucasian/blonde and higher contrast if you have dark brown or black hair for the best effect.