When it comes to being in a professional setting (i.e. a job interview etc.), I try to be myself as much as possible. Changing myself to impress others is not something I do.
I'll be polite and caring, and say things in an appropriate manner, but I never buy into the whole 'act professional' thing. I am a person with flaws, with less-than-commonly-appreciated traits; and I wont' present myself any better than I would my family, friends, or co-workers. If people can't accept me, then I have no business making an impression on them. I keep reading all these things about what you should or shouldn't reveal about yourself in an interview, how to shake hands etc., but it all seems so impersonal and fake.
I try to make an impression by doing what I feel to be appropriate at the time. I often plan what I'm going to do as much as possible beforehand, but I can't force myself to present as any better or worse than I actually am. This is why resumes kill me to write! I hate 'playing up' my good traits.
I mostly put effort into making an impression with people I view as potential friends, but who are so extroverted and fast paced they don't even notice I exist