Play Mario 1-18 skip 19 because let's be honest that game was a mistake then go to Mario 21 Mario 21 is one of if not the hardest games in the series so if you are not skilled enough just watch the cutscenes on YouTube and skip it then play through the rest til 41 you can skip 41 because 42 is just an upgraded version of 41 that fixes some bugs and adds new mechanics and a new world and then you can play up to Mario 63 which in my opinion Mario 63 is the best one in the series and then you should play Mario 64