I believe one main idea Pausch asserted was that everyone should make everything they do fun. He continually made the point that if it wasn't fun, it wasn't worth doing, because he believed life should be enjoyable.
A second main idea Pausch presented was that of living life to its fullest each and every day. He used his experiences to show that he was happy with the way he lived, because he had given everything his all as much as he believed he could.
Similarly, Pausch asserted that people must work hard to be successful. He told multiple stories of times when he lost out on something because he did not work hard enough, or times he got something because he worked hard. He is quoted as saying "Brick walls are there to stop the people who don't want it badly enough."
And lastly, I believe a fourth main idea would be Pausch's determination to find a way to be happy. He was convinced that he had to find some way to be happy and enjoy life, or it was simply not worth living. Being unhappy was worthless to him, because it made other people unhappy.