The date is going well.  You made it through your $10 plate of spaghetti, you're moving on to drinks and somewhere in-between the waitress getting your order, and the bus boy clearing your dishes, you went from being a potential lay to a complete loser. 

But what went wrong?  You were having such a good time, she was laughing at your jokes, eating off your plate.. it was the making of a perfect first date.   And that's when you open your fat mouth and say/ask, 'so you want to do this again?'

Ahhh...chickens before they hatch mean anything?  You've just gone ahead and not only assumed that the next 2 hours are going to go well (which judging by your ill-timed 2nd date question, they won't) you also handed your balls to her in a velvet sack. 

Get your poker face going.  You don't actually have to tell her what a great time you are having, the fact you're moving on to drinks should be enough indication that she's into taking another step with you.  But these are baby steps, so treat them as such.

Keep her guessing.  At the end of your date, kiss her on the cheek let her know you had a good time and leave it at 'we'll talk soon' 

DO NOT make plans for a second date at any point during your first date.  Be a little more subtle and mysterious.