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I'm running a campaign with some experienced players that is pretty complex and long-term. (Short story: Acererak is returning to the Prime Material to enslave the population, and the only weapon that can destroy him permanently is the Rod of Seven Parts.) Players started at level 1.
The players have REPEATEDLY failed to examine items and scenes where I've placed important items. This includes not looting monsters they've killed, but extends to, for example, finding a hall full of statues and not examining to note that they are actually victims of a medusa.
This has led to me having to almost spoon-feed them information and items. I even tried to "gift" them a Wand of Fireball from a party of bandits they encountered and killed, and when they failed to check for it I had one bandit survive the encounter, meet the party later, and actually drop the wand right in front of them. I had to write in multiple NPCs to flat-out say, "Hey, that vampire might not have been the BBEG" and also told them out-of-game that they need to be more observant.
What techniques can I use to have my players pay more attention to details?