Joy as a prime mitzvah, i.e. not a mitzvah to bring to any goal, but being a goal in itself. As a philosophical concept I have brought objections to this point of view. Plus there is no such mitzvah.
The other trouble is there are plenty of people for whom bringing pain to others constitutes the highest joys in life.
 . Bava Sali's primary principle was never to be without a wife. There was even a case where he got married on paper to a girl in Fez who he never saw or had any contact with. It was just in order not to be wifeless for even a short time.
 Fear of God solves the problem of short days. For instance I have found my days too short because of events which happen during the day that occupy my time and mental energy which I would have rather that had never occurred. A good solution to it: Fear of God. In my case I understood this to mean to learn books about fear of God like the "Duties of the Heart" and the Or Israel of Israel Salanter [and the Nefesh haChaim of Chaim from Voloshin--a disciple of the Geon from Villna] and I found that in fact by just spending a couple of minutes on these books per day --my entire days stated to expand and all the little things that were getting in my way disappeared.