To be any use at all, masks should have at least three layers, a scarf doesn't do anything, nor would a hijab be much help.
It makes sense to wear one when inside with strangers, eg shops, garages etc, and when they open all hairdressers will have to wear one to protect you. You should do the same for them.
Wiping the lens of your glasses with washing up liquid helps stop them steaming up, but no matter how well your mask fits they still will to some degree. Wearing them lower down your nose also helps a bit.
The number of people I see pulling down their masks to talk is incredible, if it isn't covering your nose it is useless, and by touching the front of it you have just put the germs on the front straight onto your hands.
I think the Government will see how things progress, if the numbers don't continue to go down, then it may well become compulsory in shops as well.