When Huck tells Tom that he is going to help Jim escape, Tom offers his assistance (to Huck's surprise). At this point, Tom suggests that both boys contrive separate plans to free Jim then compare their plans. Huck knows that whatever plan he comes up with will be cast aside. Tom's "superior" imagination will win out.
Huck concocts a plan anyway. His plan is very simple, requiring only one night. Huck wants to remove a board from the shack where Jim is being held, have Jim shimmy out of the hole (just as Huck himself did when he faked his death), then run for the raft and take it down-river.
Tom's plan is far more intricate from the outset and it develops more intricacies along the way.
He insists that the escape follow models from all of his favorite prison stories: he smuggles in items past the unwitting Phelpses. He makes Jim sleep with spiders and rats, and write a prison journal on a shirt. He also warns the Phelpses anonymously.
Where Huck's plan is practical and focused on the outcome, Tom's plan is impractical and focused on the "adventure" of the process.