I've found that as INFJs, we develop our Ti best when there is play involved. I would suggest...
Strategy board games like Chess, Go, etc.
Logic Games like Sudoku.
Puzzles and puzzle games.
Analyzing things and taking them apart, then trying to put them together.
Te is a bit foreign to us, and I've found that the most gains I've made in this area have been through my INTJ friends, who see the world like I do and can explain Te thinking to me in a way that I can grasp, unlike ENTJs, ISTJs, and certainly not ESTJs, who are very toxic to me. I'd suggest making friends with an INTJ, if you don't have one already. Once you get over the 'creepy' vibe they have, you'll find that they make GREAT friends for INFJs.