Shooting Walls & Floors
Many hidden passages and items are concealed behind destructible blocks. If a wall or floor looks suspicious (e.g., slightly discolored, a different texture), shoot it with your Arm Cannon or drop a bomb in Morph Ball form. This is the primary way to find secrets.
Crumbling Blocks
Some blocks will crumble and disappear when Samus stands on them for too long. Use these to access lower areas, but be careful not to fall into hazards. Sometimes, these lead to hidden paths.
Lava Receding Mechanic
The game's progression is tied to the lava levels. As you defeat Metroids, the lava recedes, opening up new areas. If you're stuck, it usually means you haven't found all the Metroids in the current accessible area.