To get through all endings you'll want to pay close attention during the sequence where you first meet songbird and reed, since these early choices set up your path. The main endings branch out from two key decision points - first when songbird asks for help getting to night city spaceport, and later during the confrontation at the black clinic. There's four main paths, but watch closely for a hidden fifth route early on.

For the crucial timing if you're aiming for the tower ending you'll need to lock in either king of swords or king of pentacles, which means siding with reed at specific moments. The king of swords path opens up when you initially help songbird but switch allegiance to reed during the clinic standoff, while pentacles requires backing reed from the start and refusing songbird's final request. Pay attention to the dialogue choices with reed especially after the clinic - picking certain responses can lock you out of the tower completely. Specific weapon rewards like reed's unique pariah pistol depend on your choices too, so consider what gear you're after.

Quick note that if you want the secret fifth ending, you'll need to make your move right after the first reed meetup - there's a specific dialogue branch that lets you bail on the whole mission then and there. Just keep in mind this cuts off access to most of the expansion content and rewards, so timing this one is pretty situational.