In terms of making the date special, I would suggest thinking about something that is memorable to either her or the both of you.
Such as a spot that you first met her at, the place you first kissed, where you saw your first movie together, etc.
Re-visiting the fond memories of the past can be quite the 'memorable' experience.
And if you can find out without letting her know or if you already do know, think of things that she's always wanted to do, but never has had the chance or opportunity too.
Even if it's something that's impossible to do at the time or because of short notice, that's when you can get creative and fun, then explain the meaning behind what you did, how you wanted to give her something that she's always wanted.
Walk in Peace.