Germany is no Scandinavia or the Netherlands when it comes to speaking English. So don’t assume that all Germans speak good English, even though many make some effort to do so. The younger generation and people working in tourism will definitely have at least a conversational level of English, but don't be surprised if you go to a pharmacy to buy something and find the pharmaciest not being able to say a word in English.
Germans, however, will really appreciate the effort if you try to speak German with them, even if you do it badly. Do note, that formality in German, is still valued and, in particular the use of ‘Du’ and ‘Sie’, meaning ‘you’. The former is informal, or used when talking with children, and the latter the more formal version. Unless someone uses ‘Du’ with you, stick to ‘Sie’ when talking to strangers.
Here are some basic phrases you should learn before travelling to Germany.
Guten Morgen – Guten Tag – Guten Abend – Hallo = good morning – good day – good everning – hello
Wie geht's? = how are you?
Danke – danke schön/vielen dank = thank you – thank you very much
Bitte = please
Entschuldigung = excuse me
Könnten Sie mir helfen? = could you help me?
Sprechen Sie Englisch? = do you speak English?
Wo ist...? = where is..?
Tschüss = bye (informal)
Auf Wiedersehen = goodbye (formal)
Note that it is the norm to say hello and goodbye when you enter a shop or office. So, Guten Morgen, Guten Abend in the morning or evening respectively and then Tschüss or Auf Wiedersehen for goodbye.