Select a suitable location
Try to choose a place where she will be able to cope with the unpleasant information. If you choose a restaurant, it would be a blow below the belt, because, for example, if she starts to cry, will be exposed to a humiliating close views due to neighboring tables. Also, it is not appropriate to tell her about his decision in the place of your first date, or she is as sentimental value. At least, do not spoil her memories.
Select the appropriate time
Holidays, birthdays, anniversaries and other similar events are the best opportunity to acquaint her with the fact that she will never see. In fact, whether you want to have Christmas at her forever associated with the breakup.
Do it personally
You may have the desire to avoid unpleasant confrontation and leave by phone or by mail. Take courage, and tell her in person. We are talking about a minimum amount of decency and respect that she can be.
Be honest but sensitive. If she starts to ask questions, honestly answer them. Be sure that it is required to know about the cause of the breakup, and will hate you even more because you lied to her. On the other hand, do not need to explain to her that you are breaking up with her because she is completely incompetent "Board", and your new hobby – it's just a hurricane.