To begin with, if you do not wear glasses before, then it is best to consult an ophthalmologist, do not try to pick up points on their own, and even more so do not use glasses friends or relatives. Also proceed in the case, if the glasses that you always had suddenly ceased to be effective or cause while wearing some discomfort. Also re-check with your doctor if you get a new pair of glasses a year or more after visiting a specialist.
If you wear glasses for quite a long time and everything is in order, and you just decided to buy a new, try to choose the right frame that fits your type of appearance, but note that the shape of the openings would practically be different from the shape of openings on your old glasses. Ask optics check the fact that the lenses are in the same position and at the same distance from the eye, as in your previous glasses.
If ordered glasses cause discomfort or do not provide the desired view, refer to the optician and ask them to check whether the data glasses prescription. If the error is not possible, then go to a specialist who prescribed you the data points and do not forget to bring your old glasses, prescriptions written and the conclusion of an ophthalmologist (if any).
If new glasses have a number of differences from your old glasses, you will need some time to get used to them (about two weeks). If after this period (at constant wearing) and you are not accustomed to the new points, check with the doctor who ordered them to you.
Choosing a lens for new glasses, be aware that plastic versions have the same optical qualities as glass, but they are easier and safer, since almost never fight.
Also keep in mind that the lenses can be different cover, it can affect their scratch resistance, to prolong their life and improve vision in bad weather, etc.
You can not order points, and buy ready-made, but before that you should consult with an ophthalmologist and get his recipe (note that in the recipe should be prescribed lenses of equal strength, not more than ± 3 D). Ready goggles buy only in specialized stores, otherwise you risk getting poor-quality goods.
Remember that the glasses become your companion for many years, their convenience will largely depend on your mood and performance!