This depends on the healthcare system of the country and such, but if you can plan it with your family doctor or a specialised one the chance of success will greatly increase and the toil on your body from withdrawal will be reduced. Or simply having someone with you to console you. The first week is the toughest if you go from 100 to 0, but after that you'll only feel better day after day. And, of course, for a time don't go out to talk with those who smoke, it'll only make it harder. I can only add that I know people who managed to quit after forty or even fifty years of smoking and they became cheerful, more active and fit.