Biggest differences for me
Sharing the build of cities so that I benefit from other players effort. I do this more than I would in 2 player. If I can share separately with at least 2 opposition players then I am happy I am out scoring all 3 opponents if the cities are completed.
I put fccc tiles near opposing player cities but don't place meeple to try to stop opponent cities being completable.
I get an early farmer in place and glom a second towards end of game to win a farm. In 2 player I would usually wait till later to do this.
I don't tend to place tiles to trap 1 meeple of one opponent ad it does not affect the other 2 players, rather I would enhance by own scoring which gives an advantage against all 3 opponents.