More than anything do it nice and slow. Be pragmatic, don’t force them to read things you know they’ll hate/things that call them dumb for having that opinion. I find that being caring and respectful while still being honest with your opinion helps. It sounds contradictory but if you explain in a way that makes them understand Leninism better rather than a way like Anarchism or Socialism, which is my favorite book mind you, but Stalin definitely laughs at anarkiddies and shys away just short of calling them dumbasses. Great read tho, and later into their journey into Marxist Leninism if they go further down that path Id suggest that book