I definitely would recommend in-game trading (if you are patient have time to do it) or selling collectibles. Posting works too, but you can get TBT quicker with those 2 other options. I also know some people make TBT by selling art on here as well (avatars, signatures, etc.). Out of all the methods I mentioned though, collectibles are the best way of amassing large amounts of TBT + its fun and far less time constraining in comparison.