Impressing an interviewer, especially on technical subjects is largely beyond your control.
However, when sizing up a candidate's potential 'cultural fit', hiring managers still tend to hire people they like.
Being likeable, that is being friendly-- can go a long way creating a favorable impression. Express a genuine curiosity in the individuals you meet with and what they do, ask intelligent questions, try to find common areas of interest.
In sales, they call it rapport building-- it's a practiced skill-- tremendously powerful and underappreciated asset.