As a full-time glasses wearer for the last 40 years, this is my advice:
Try on a good selection of frames, even those you don't think will suit you, and take a photograph of yourself in each pair. Go home and browse the photos to choose at your leisure.
Remember you don't have to get your glasses from the same optician that gave you your prescription, so if you find nothing you like, try elsewhere.
Two-for-one offers are very much worthwhile as you can choose two different styles for different occasions/outfits/moods. It's worth getting one pair as 'transition' lenses (they adjust to sunlight so will serve as prescription sunglasses).
Spend as much as you can afford, do not skimp, as your glasses will be part of your face, one of the first things people see.
If you have a straightforward, single-vision prescription, you can buy extra pairs online very cheaply; e.g. Glasses Direct They're not as good as properly fitted glasses in my experience, but can give extra choice for occasional wear.