For resources to learn German, please consult this question: Resources for learning German
But you don't need to learn German if you speak English and want to travel to a German-speaking country as a tourist, or if you just want to stay for a few weeks or months. People in Germany, Austria, Switzerland and everywhere else where German is spoken learn English in school for 8 to 12 years. Only older people (70+) have poor English skills, but everyone else speaks English quite well, especially younger people (under 40) and anyone who has a job that brings them into contact with tourists or other foreigners.
It is only necessary to learn German if you plan to stay in a German-speaking country for a longer period of time, because all the documents you will receive from the authorities when you move to a German-speaking country will be in German.
So the best strategy may be to come to Germany and learn German by talking to your new neighbors and work colleagues if you have a job here (for which you need a work permit in advance). What will also help you is listening to German radio stations, reading German newspapers and watching German TV.