Look in the archive under 'cultural differences' / 'kulturelle Unterschiede' -- there should be several threads, some of them quite long.
One aspect that's been discussed a lot here in the forum is the phrasing of requests. Subjunctive forms like 'could' and 'would' are very common in polite English; 'can I' or 'do you want to' can sound more offhand or less respectful. But apparently literal translations with the subjunctive can sound a bit overdone in German, which tends to prefer 'kann' rather than 'könnte' (if I understand correctly).
Other differences are also often just a matter of degree. For instance, we are capable of saying a straight yes or no if you insist, even if we beat around the bush a bit first to take the edge off. Often in English it's understood that the first question and the first answer are more general, casual, tentative, noncommittal. That avoids putting anyone on the spot or seeming too pushy, and it allows for casual conversation in passing to take place at a rather superficial level without requiring too much effort from anyone. But if someone really wants an answer, they'll insist, and then you can say, 'Well, if you're really sure it's not too much trouble, I'd love to, thank you very much' or 'Well, if you really want my honest opinion, I'm afraid I still see several problems with ...'
In some cultures, though, 'no' is simply never an acceptable answer, even on the second or third asking -- it's better to lie than ever to hurt someone's feelings by refusing an offer or a request. To me, that's too indirect. (-: That is, along a spectrum of indirectness in all cultures, we're probably somewhere more in the middle than totally opposite to German speakers.
I agree with the others, though, that pointed questions or judgments about personal health, appearance, etc. are pretty much no-no's. Here's an example of how we might address the 'Your hair looks terrible today' concept:
Hi! How's it going? ... You look a little tired. Are you having a rough week? ... Oh? Yeah, that deadline is really a bear, I'm under a lot of stress right now too. Say, did you do something different to your hair? ... Oh? A new haircut? That's nice. ... Like it? Well, you know, now that you mention it I think I sort of liked the way you had it before better. But maybe the new look will grow on me. (-:
Of course, this is not in the end necessarily much less truthful, since everyone knows that 'You look really tired' is often just a euphemism for 'You look terrible,' but somehow it doesn't feel quite as hurtful.
That said, my observation just from here in the forum is that the range of differences among personality types is almost as wide as the cultural difference itself. That is, there are plenty of blunt English speakers and plenty of polite German speakers, so generalizing isn't necessarily that productive because the exceptions always overlap.