Actually, I think first timers should go slower, otherwise it gives the impression running is easy ..
And wear a big red L plate, so everone knows you're a learner & have a chance to wind you up a bit,and of course, a green P for the next 6 races.
Brian - less than 1:12 and you can probably start making a living from it (or at least get lots of free kit) ... more than 3:30 and you might be walking. Anything in between is normally OK. Take a look at the results for last year, and see the range.
(Although my first ever half is still my best time, it's all been slower since then. But I got very close Sunday ...if it wasn't for that headwind in the last 2 miles, or those hills, or....)