We can learn a wonderful thing about the Yetzer Hara and how to fight it from the Baal Shem as brought in Keser Shem Tov. He says there that the way to defeat the Yetzer Hara is through using its own arguments against it. Seeing that the Yetzer Hara is sent by Hashem to fulfill its own purpose, it very much wants to do its job and get a person to do an aveira (sin), so from this we can learn a little Mussar that we should want to fulfill our holy mission from Hashem which is specifically not to sin and to fulfill mitzvos.
One additional aspect we can learn from this particular lesson of the Baal Shem Tov has to do with the concept of serving Hashem b’simcha (with joy), and being b’simcha even in times when not specifically involved in doing mitzvos. There’s a tefillah based off the idea that we should dedicate each and every action we perform throughout the day, with every thought and word we speak, l’shem yichud Kudsha B’rich Hu U’Shchintei (for the sake of the unification of the Holy One Blessed be He and His Shechinah). Considering this is the essential point of all forms of avodah, every mitzvah, every bit of Torah learned, according to the sifrei Kabbalah, then every action of our day becomes avodas Hashem. From this perspective we can very easily have a day full of simcha, keeping this in mind and genuinely dedicating everything to avodas Hashem.
Yismach Lev 