Junk - Screens 1, 2, and the Elevator
This stage heavily utilizes the Thunder Strike. This is also Junk Man's weakness, so make sure you save enough for the boss.
Screen 1
Quick Swap to Thunder Strike. Slide, jump, and shoot/zap the first flying enemy.
Jump the pit and slide off the ledge, then shoot-slide. The bug should get zapped where a lemon would fly over its head.
Continue sliding to the end of the low floor, then full jump on top of the bug-junk-house. You don't need to destroy it and you can walk (and slide) on it.
Climb and fall down the ladder.
Screen 2
Slide through to the elevator door
The Elevator
Just hang out in the right corner and dodge things. Get through the door on the right as soon as you can.