Does anyone have personal/practical suggestions of how to increase one's simcha in Adar?
The short answer: Get ready for Purim, by learning about why Purim is a joyous day and start internalizing those happy lessons.
I already wrote here, about 2 reasons why we increase joy in Adar - as a preparation for Purim. To recap:
According to the Michtav M'Eliyahu (Vol. 2 pg 125) the happiness we feel on Purim is a הכרת הטוב - recognizing the goodness - of the miracle of Purim, which is all about revenge. HaShem took revenge on Haman and ונהפוך הוא - turned the tables - and made Mordechai the Prime Minister in his stead.
The joy required to celebrate this הכרת הטוב efficiently requires work and preparation, continues the Michtav M'Eliyahu, and one needs to start this preparation as soon as Adar starts, in order to be in the right mood when Purim arrives.
The Ramchal (Derech HaShem ח"ד פ"ח) says that the point of the joy of Purim is the קבלת התורה - celebrating the re-acceptance of the Torah.
Practically speaking, you could start by studying the above 2 passages, to gain a better understanding of the reason behind the joy of Purim and how to prepare for it.
You could then learn relevant Midrashim on the Megilla related to the ונהפוך הוא and the קבלת התורה .