I have to say that at the moment, I wear my glasses more than contact lenses. Mostly because I can't be bothered with putting lenses in, taking them out, cleaning them etc. so glasses are just a quick and easy way to make sure I can actually see where I'm going! Wearing glasses with hijab can sometimes be a pain as the arms of the glasses are squashed between the back of your ear and your head, leaving you with a headache/earache and a not very comfortable hijab. Also, if your frames are wide from the front, they can create a gap, which may mean that the odd hair will come loose.
Here are some idea's that have worked for me (and can also apply when wearing sunglasses). Let me know if they help =)
Wear your glasses over your hijab. Now I'm talking about after you've pinned under the chin/wrapped the hijab around once, then put the glasses on and carry on wrapping your hijab. This way the arms of the glasses are not in direct contact with your skin (so no more pain) and there is no risk of any hair showing from underneath. Also, this style makes is a lot more practical if you have to remove your glasses as they simply slide back in. Perfect for when it's raining and you need to wipe your glasses in order to see again!
If you're not keen on wearing the glasses over your hijab, then I would most definitely recommend wearing them over an underscarf. I use tube underscarves as they don't need to be tied at the back of the head, and again don't cause earaches. They are also a lot easier to put on as they are pretty much a supersized hairband. Simply wear the underscarf first and make sure that your ears are at least partially covered (so that the glasses don't touch your ears/head) and then wear the glasses. Wrap hijab as you normally would.
Here is a few hijab tutorial that I've come across which may also help =)
Any other tips that you'd recommend for glasses wearing hijabi's?