Ride the Switchboard at the beginning and dodge the cannons and Parabone, until you reach a circular platform with a ?-Block. Hit it to collect a Cannon Box that you will need throughout this level. As you move around the loop, fire a charged cannonball into the ?-Blocks across the way to extend a platform to the Stamp, then quickly return so you can reach the main area. When you reach the large chunk of land, you will encounter more cannons, as well as some Spinies. The wall ahead has some cannons shooting to the left and right. You will need to use these cannonballs to reach the top, but you also will need the Cannon Box.
Once you do reach the top, go to the right side and blow up the cracked wall there to reveal Green Star #1. Enter the green pipe to come to a swimming section that will autoscroll. Eventually, you will see some bricks along a wall on the bottom of the screen, so blast through them to find Green Star #2. The clear pipe at the top of the screen in the same area has a clock pickup. Upon exiting the underwater section, you will be back on dry land, with more Switchboards and the Checkpoint Flag. Here, you will need to shoot the colored blocks to make the tracks switch over, allowing you to continue.
Hit the second one you come across, then ride the Switchboard north and shoot Green Star #3. If you don’t, you won’t be able to collect it without falling into the abyss and losing a life. Return to the main path and use the various !-Blocks to let you continue and reach the end. If you don’t have a Cat Suit, then you will need to use cannonballs to get the top of the flagpole.