Energy Farming
If your energy is low before a tough Metroid fight, find a room with easily defeated enemies that drop Energy Balls. Repeatedly enter and exit the room to respawn enemies and farm energy until your tanks are full. This is a crucial survival tactic.
Missile Conservation
Only use missiles on Metroids and Missile Blocks. For regular enemies, rely on your Arm Cannon. If you're low on missiles, farm them from enemies that drop them, or revisit areas with Missile Expansions you might have missed.
Save Point Strategy
Always save your game after acquiring a major power-up or defeating a Metroid. This prevents losing significant progress if you die. If you're about to enter a challenging area, find the nearest save point first.