I don't go by first impressions. I do go by how they treat strangers though.
Usually if I'm on a date and the guy tries to impress me by... for example... ordering at a restaurant and telling the waiter what I will have after I told him what I was going to get the impression fails. Just seems controlling to me. I had a different date drive by a house and tell me that lived there which I really didn't care.
I also don't like stupid arguments when I'm just starting to get to know someone. I say this simply because I was on a date about a month ago and after I told him I had moved to California in 1999 and moved back at the end of 2002 and it was 4 years he kept telling me it was only 3. Like it was a big deal. Technically yes it wasn't 4 years. It was 3 years and 11 months but geez.