Newer (& some older) are looking for some magic recipe & often trying to force the situation instead of waiting to look for good spots (will take some time & experience to identify those 'spots').
The only advice I could offer would be to ... learn.. learn.. learn some more.
ie. stack sizes and how we need to adjust as a result of
- potential steal spots
- good 3-betting spots
- resteal shove spots
- knowing when it's +ev to call off
- understanding ICM & realizing how it affects the situation
.. etc. etc. etc. etc.
Identifying good players & identifying their ranges in certain spots (ie. good players don't typically flat with 15-20bb's over an MP, HJ, CO raise in pos. unless they're holding a MONSTER).
The list goes on.. & on & on.
Try watching some vids., some live streaming (even the WSOP
final tables as the commentary this year is superb by some of the guest players in the booth.. ie. Brian Rast & many, many others). Try reading some decent books (ie. WinningPokerTOurnaments - One Hand At A Time)
I think for us to say, "what do I need to do in final 20 players" is actually a vague question because as always 'it depends' (there are always many variables).
If you want to discover what mistakes you might be making, post some of your MTT HH's for feedback.