That's a million quid question.

I can remember being diagnosed as pre-diabetic. I was diagnosed as Type 2 some 15 years later.
The only advice I got when I was diagnosed at the time I was told I was 'pre-diabetic' was just that "Watch those Carbs". Not much help when you're an athlete living on Pasta !

The answer is - it depends. I can only tell you what I wish I'd been told in retospect, and what works for me.
I suspect I'm correct in guessing that as a pre-diabetic, you aren't on any medication? That can make a difference.

The problem is that what carbs work for you depends on a lot of factors. Your body mass, the amount of excersise you take,
what you like to eat, and how much how often. Being pre-d, it's also difficult to judge just how your well bod is dealing with
carb products. The bad news is that your body at the moment is dealing with carbohydrates inconsistently. I'm assuming you
don't have any serious health problems.

First thing to do is to get yourself referred to a dietician by your Doctor, and discuss those factors with her (it always seems to be a her :) )

You can help yourself by getting your Doc to prescribe you a blood sugar meter. I'm not not going to recommend any particular one.
Being UK based (you don't say where you're from) I was offered a choice of an NHS version for free, or some money off vouchers.
I went for the vouchers and got one for the princely sum of £5. I think even if you went out and bought one, it's cost little more
than £15. There are some serious financial advantages in the UK to have the GP prescribe one, which I'll get to that in a bit. But not
least that the test strips, lancets and recording booklets are on prescription.

I'm not sure that this would strictly apply to you for an extended period, but I suspect it might be helpful in the short term, assuming you
are having regular GP appointments. Having a meter, and following the instructions carefully, check your blood sugar (UK mmol) before
breakfast, after a midday meal, and about 2 hours after an evening meal. I'd also suggest that if you like a beer (or whatever) that when
your sure you aren't going to drink anymore - do a test then. After you've tested, make a note of the figure you get. There'll probably be
a record book provided.

I think I'm right that for non-diabetics 8-10 mmol, and up to 11 or so occasionally is cool. But you might get much higher or lower. Surprisingly,
after a beer, you might find it drops. Don't let that fool you - that, on balance, is not good. If it was, I'd live under a table :) It's not good,
because alcohol can cause blood sugar levels to drop too far.

If you do that for - I dunno, maybe a month? - you'll get an idea, with your 'normal' diet, what your blood sugar levels are. The chances are they're swinging between 5 to maybe 18 or higher. Now you need to reduce carbohydrates, still testing, until you can keep your blood sugar levels between about 5 and 7 or 8.

And finally...

The term Pre-Diabetic is a pain, because it's just a way of saying "considering your family history, and the tests we've done, your at risk of becoming diabetic". It's a fluffy diagnosis in my opinion. You don't say whether your relatives are Type One or Type Two diabetics. Type one's inject insulin. But I have Type 2 mates that do too. I think it's fair to say that for all practical purposes, Type One's test their blood sugar levels prior to a meal or alcohol to determine their blood sugar levels to decide the insulin they need. Type 2's use blood sugar levels to determine their diet over time to manage what they eat in the context of the meals they eat and the tablets they take.

In the UK, the upside is that being diagnosed as diabetic is that the meter, the strips, recording book AND ANY OTHER medication entitles you to a medical exemption certificate - form available from a GP Practice, which entitles one to a little white plastic card which gives you free prescriptions permanently.

I've skimmed over and generalised a lot here - so if anyone wants to add/disagree - feel free!