A true speakeasy. Finding the hidden entrance is fun, but showing a first timer the way it's even better. Don't tell them where you're going and watch their face light up when the intercom goes off, signaling they're coming to open the door for you. That's also another great touch, for a place to take the time to individually lead in every customer, giving opportunity for a small chat and maybe explanation of the bar.
When it comes to ordering, do yourself a favour, let the bartender decide. Give them a general guideline (e.g. Tequila based, sour, and not boozy) and watch them work. These guys know their stuff and their range of ingredients is crazy. If there's an alcohol you don't normally like, this is the kind of place that can change that for you. Be adventurous, you're in good hands.