Taking lots of photos with the frames on is useful - the mirrors show the reverse of the photos so it's always a bit of a surprise when I see the frames in photos and see what other people see (also I can't see well enough without my glasses to really see myself!).
My eyes are too bad for any of the online sites to accept my prescription sadly, but it can be good if you don't have a very complex prescription. However, if you have much in the way of astigmatism etc, it's really important the they fit exactly as even slight differences can make it look all wrong. So I'd be careful about using them unless you have quite a straightforward prescription (which you probably do, if you've not needed them before). For complex prescriptions, thinning lenses makes a huge difference, but not so much for straightforward ones. The shape of the frame can also make a difference, depending on e.g., the angle and degree of astigmatism. They can hide the thickest parts of my lenses by being careful about how they are fit into the frames as well, and some dispensers are much better at that than others. Again, probably not an issue unless you end up with a bad astigmatism or something. The size of the frame matters as well for things like that.
If you get them at the optician, they can adjust them for you, and you can go back as many times as needed. Often they seem like they fit fine at first (bit like shoes), but then later you realise you have nose dents or whatever, and they can adjust them again. Or if they really don't seem to be right, prescription wise, you can go back - I've had to have them redone occasionally (again more a problem with bad eyes). They will also replace or tighten screws for you at any point afterwards.
It's actually much easier if you have to wear them all the time, as you then just get used to it, and don't have to faff around carrying a case and remembering where you've put it!
Anti fog and anti scratch coatings are good.
There is probably a dispenser at the opticians who is quite good at advising frame shape based on your face shape, etc. Different places have different brands, so if you have a brand you like and your optician doesn't have it, you can still go to another place (in person) and try their frames. I find that the independent opticians have nicer frames for what I need than specsavers etc, but the two main opticians here do carry different brands (i liked ones by Bevel).