1. Be optimistic when setting high level, year-long goals. But be pessimistic when drawing out all the implementation details of what you'll actually have to do to achieve those goals.
2. Be pessimistic about the difficulty of anything you want to achieve, but optimistic about your ability to conquer those difficulties.
It have citations and is written by a psychologist. However, I did not have a lot of time to compare notes between books written by other psychologists in the field.
The thing is, being a specialist means you don't spend much time scrutinizing what is wrong and not wrong in their studies or books in other fields. You sometime have to trust scientists for being scientific.
My recommendation is this book:
It cited real world scientific research and gave practical advice on how to set goal and to succeed at one's goal.
Disclaimer: I am only aware of such knowledge, not actually putting into practice said knowledge. Currently, my only implementation of scientific self improvement is spaced repetition, which simply exploit the fact that we retain more information learned over a long period of time.
Amazon links: http://www.amazon.com/dp/0452297710 and http://www.amazon.com/dp/0143122231
Thorough book notes: http://www.quora.com/Leo-Polovets/Exceptionally-long-book-no... and http://www.quora.com/Leo-Polovets/Exceptionally-long-book-no...