True Adventurer is achieved once you collect a certain amount of studs in a level so through out the level, you should work on smashing everything that you can smash and get as much studs as possible. As you collect studs in levels, you will see the the True Adventurer meter letting you know how far it is from being full.
This is much easier (and quicker) with the more multipliers that you have. I went to the last level I needed for this achievement with all multipliers and I literally got True Adventurer the very second the level started. Once you gain your last needed True Adventurer, the achievement will unlock.