Plumbing P-traps should be full, or the building will pull in sewer gas during the depressurization test.
Any Large perforations in the drywall such as drains and electrical panel should be foamed around.
Exterior doors should have their hardware installed and properly seal shut with weather stripping.
Any access hatch to the crawlspace or attic should have a foam or rubber gasket seal.
Problem areas beyond these are usually things like can-lights not being foamed or caulked around, the baseboard trim not having caulk underneath it where the drywall meets the floor, and sometimes microwave vents don't have a good enough seal around them.
The baseboards being caulked is the big one that solves the most cases of people having trouble getting a passing score - by the time a building is ready to be tested, it's too late to go back and caulk the drywall to the plate (many people forget or neglect to do so), and since the attic is ventilated to the atmosphere, that provides a large channel for air to get in through the walls, flowing in from around outlets, under the baseboards, and through any other perforation in the drywall. This is often the source of bad scores because all of those small openings stack up into a large Total Leakage Area.
In many cases, since the baseboards are usually already installed at test time, it is recommended to buy a few tubes of clear acrylic caulk (the cheap stuff is fine), and caulk the top and bottom of all baseboards. It always makes a big difference.
