In Smash TV, the best policy is to keep moving and never get too close to the doors with your back turned; you never know when they're going to open.
The default machine gun doesn't hurt the bosses (notice how bullets ricochet off of them). You need to get a weapon power-up to do real damage.
Pay attention to the map when it pops up, and plot your navigation through the rooms so you can hit the bonus room.
Smash TV is best played with two players. There are too many enemies to count, so a mix between cooperative (covering each other's backs) and competitive (snagging the bonuses) play is best.