- The "light world/dark world" mechanic is pretty cool. Remember that things you do in one world may change the local situation in the other. Also, if you get stuck and don't know what to do, try backtracking to all the portals you've already used if you've gained new abilities since you last visited. Lots of goodies can be earned that way, and new paths may be opened.
- Don't be afraid to retreat to the light world periodically to recharge your energy/ammo during the early game. There will come a time when it's not necessary, so don't get too stressed out about the fact that the very air in the dark world will kill you more quickly than most enemies could.
- The ammo system is kind of wonky. Killing enemies/breaking containers with the light gun yields dark ammo and vice-versa. And if you run out of a type of ammo and need to open a door, don't worry - charging your gun will allow you to fire one normal shot at a time of the light or dark beam.
- One nice thing about the ammo system is that, unlike most power-ups, the light/dark ammo will automatically be pulled towards you as if you were using the charge beam. There are also countless respawning containers everywhere in the world. Keeping that in mind, it should be very easy to keep your ammo full while running around the map without even having to slow down. That also means you shouldn't be afraid to use your light/dark ammo on normal enemies.
- Crates might seem useless/empty at first, but they actually give you the things (energy/ammo/missiles) you lack most at the moment, and shooting small crates with light/dark beam is a great way to get opposite-color ammo quickly and safely.