The Mega Buster can't be charged in this game, but the Magma Bazooka can be charged! Just hold down the button you use to fire the weapon & Mega Man will begin to glow. Using charged shots from the magma bazooka helps a lot when facing bosses that are vunerable to it, such as Hornet Man, & the flower mini boss. Note: using charged shots obviously depletes ammo a lot faster.
Want an easy way to produce more screws, power-ups, & 1-ups? Well go to any level that has a mass enemy appearance (Plug Man's stage, the round enemies that come out of the pipes, or Tornado Man's stage, the umbrella enemies). On Plug Man's level, just go to the end of the first screen where there's two pipes, & a big screw underneath one of the pipes. Stand on the edge of the higher of the two pipes & deploy your Jewel Sattelite weapon. Just stand still & let the infinite amount of round enemies float into your gem shield, they'll eventually drops items you can collect, such as screws & extra lives. To do this on Tornado Man's level, get to the area where when you jump, the wind will push you into the right direction. Use the Rush Coil to get the 1-up on the high platform, then stay on that platform & deploy your jewel sattelite, an infinite amount of umbrella enemies will touch your gem shield & die, thus eventually producing items for you to collect. This is a great method to get extra lives without buying any, & also a great way to increase the amount of screws you have.
There's an easy way to defeating the fire dragon mini boss in Magma Man's level. The Black Hole Bomb will become your best friend here! Place a black hole bomb in the middle of the screen everytime the dragon flies across the screen; not only will this damage the mini boss, but it will also suck up all of his fireballs, which means you're out of harm's way! This is also helpful when fighting the dragon again in level 1 of Wily's Castle.