Hi Anja,
I always liked the One Minute Manager series started by Ken Blanchard. The idea of not labouring a point but getting it said, understood and then positive action in a short time was particularly good. Also the model of Situational Leadership for helping to to motivate staff at different levels of development in specific tasks is excellent.

Cheers
Andy

One from the list of NLP presuppositions, but an ex-manager of mine used to pin it up whereever he worked (long before I know about NLP)...

If you always do what you have always done, you will always get what you already have.

Cheers
Andy