Collect the key in the well, then jump to the top of the pyramid on level 3 as soon as possible.
Cheat
On the first level, if you get to the end of the landscape in under 8 seconds there will be a rocket there. Jump on it for a ride to level 8.
Level 3 warp
There is an easy way to get to level 3 , on stage 1 go to the first island (made up of 1 square) and it has nothing on it just plain grass, then press A and B at the same time and you should go through a hole to level 3.
Unreachable items
Allow the shark to catch you on levels 1 and 2. It will eject you into the air and allow you to reach the items that were previously too high.
Yellow fish and extra life
At the very end of the level 8 (the fish level), do not go into the door, but instead go back. You should see a flying carpet, like in level 5. Get on it, and get the clock before you get the extra life. After you get the extra life and are in the water, all the fish will be yellows. Also, If you swim alongside the spikes, on the ground in the lake, is a hidden extra life.