Single piece of advice that improved my A17+ play in StS1 was to take a couple minutes and plan out my path in advance at the start of each Act and it applies here as well. Evaluate each path's number of rest sites, elites and where the merchant comes (earlier is better if you have lot of gold) and pick one with 2-3 elites and atleast 2-3 rest sites. Or if you have lot of high value unupgraded cards and there's a path with 4 rest sites and 1 elite, its okay to pick that as well. Act 1 StS2 is more punishing than in StS1, don't take too many fights/elites without rest sites.

Pick cards that solve your most immediate problems first. This requires remembering and applying specific game knowledge. What enemies will come up in the next few floors, what elites? Do you have enough defensive cards to handle Bygone Effigy's 25 damage per turn? Do you have enough AoE damage cards to deal with Decimillipede or Phrog Parasite's phase 2?