This may be obvious, but you need to GENTLY run your fingers inside the tire - you don't want to slice your finger on the same piece of glass that started this whole mess.

I love the idea of leaving the stem in place while fixing the flat. Much quicker, and much easier to know exactly where to check the tire for the culprit. I second the idea of lining up the label with the stem valve, but this is fool-proof.

Finally, practice, practice, practice. I have a bike that I rarely ride, but I have one tire for the road, and another for the trainer, so I change it often and I've gotten MUCH better at it. Even did it for the first time last week without levers. Can't figure out why I was so proud of that, but I was!