You might first want to take a bonafide personality test, such as the Meyers-Briggs Type Indicator or the Enneagram Indicator. Both are available online for free at various sources so do a search. Knowing what basic personality you have will form a good foundation.
I am "INTJ" (Meyers-Briggs) and a "Four with a Five wing" (Enneagram).
Whether you do the personality tests or not, the next thing you should do is think of some guy you admire. Perhaps a movie star or singer. Maybe this guy is suave, cool and charming. Let's say you admire George Clooney. Okay, go rent a few George Clooney movies, the ones where he's really cool. One great example is "Ocean's Eleven".
Try to pick up on his body language, his facial expressions, how he looks people in the eyes, how he talks to people, how he dresses. Make note of all of these things.
Then decide which things about him you wish to emulate. "BE" your chosen hero for 3 days and see how it feels. If it works well, decide to "be" this person for exactly 21 days, because it is proven that if you can change your patterns for at least 21 days, it will begin to transform you. Less than 21 days doesn't work and any time over that is even better.
You get the idea.
And congratulations for wanting to change. It's a sign of health.