What kind of improvement should I get from glasses? How far should I be able to see clearly?

Is this your first pair of prescription glasses? I am guessing that it is not. Do you see better with your new glasses than you did with your old ones? If so, that is a good sign. It is impossible to tell without examining your eyes if your glasses are the best they can be for you. People whose prescription is as strong as yours often have other limiting factors on their vision. At the very least, your prescription makes things smaller as it makes them sharper. If this is your first prescription, your world has been rocked enough for now. If you are replacing other glasses and see significantly better than you did with your old ones, the new prescription is probably perfect for you.