The fundamental thing I did in order to learn tlhIngan Hol was to practice it with other people.
I joined the
tlhIngan-Hol mailing list and read everything people were writing. I tried to add to the conversations, and got appropriately helpful feedback when I made mistakes. At one point I recorded a journal in Klingon during a week of vacation and submitted each day's entry to the mailing list, again getting appropriately helpful feedback.
My first big leap in skill occurred when I joined the Klingon Education Virtual Environment MUSH and began interacting with people in real time. That resource is, alas, defunct. The second major event in my learning was when I attended
qep'a' wejDIch, the Third Great Meeting of the Klingon Language Institute, and got to talk to people face to face. The annual
qep'a' is now a permanent part of my summer vacation plans.