A few ideas:
1) Do you get enough sleep? If you never get enough sleep, it may be hard to be in a good mood while davening shacharis.
2) Do you drink coffee or tea before davening? If not, consider it, because a little caffeine can put you in a good mood.
3) If I recall correctly, Rambam says we should sit and meditate an hour before and after davening! If that’s what we’re really supposed to do, then surely we can manage to spend one or two minutes meditating before davening. Close your ideas, clear your mind and try to concentrate on love and yearning for Hashem. (“To you, Lord, I lift my soul” — Tehillim 25.) Learn more about meditation from kosher sources such as R’ Aryeh Kaplan or R’ Dovber Pinson. Meditation can be extremely enjoyable, so making your davening like a meditation should help.
4) Spend a minute or two, or even just a few seconds, of personal prayer in your own words before davening, or in the middle of davening, between sections. Ask Hashem to open your heart and allow yourself to pray with true kavanah and devotion. If you don’t have time during davening, pray at some other time during the day for a few minutes, asking Hashem to let you serve him with joy. Check out the Chofetz Chaim’s quote on hisbodedus (search using the term hitbodedut on google to find it easily online), or the sections on tefilah and hisbodedus in Likutei Eitzot.
5) Do you daven with a fast minyan? Maybe you could find a slower one?
6) Start on the section of davening you identify with the most, and try to do that with as much feeling and kavanah as you can. Then expand that slowly to other parts of the service.
7) Spend a few minutes before davening thanking Hashem for all the good things you have and that have happened to you (and even for the seemingly bad). There’s tons of empirical evidence from psychological studies that gratitude makes you feel happy!