World 1-7
For nearly unlimited lives in world 1, try this:
Grab one of those baddies that roll up in a ball.
When you get to a point where you see the middle ring, don't go to it. Instead, go to the other side of the pipe that you just went pass.
When shyguys start coming out the pipe, spit the ball out.
Grab the ball before it stops rolling. Repeat the same process over and over until you gain some men.
If you wait until the ball stops you'll have to do the process again. The same thing goes if you destroy the ball and you'll have to grab another one.
Another problem is if you're not standing on the right spot. If you're not, the ball will go over the pipe instead of bouncing back and forth between the pipe and the stuff you can destroy with your eggs or by ground pound.
World 4-1
To gain all the lives you want, try this:
On Stage 4-1 (with at least 3 eggs [maximum 5 eggs]), grab a shell. But do not make a egg out of it.
When you get to a point where there's two tunnels with piranha plants, kill the plants with the eggs.
Stand on the tunnel facing the pipe with the shyguys jumping out.
Make sure that the shyguys are jumping out the tunnel. Then spit the shell out.
The shell should go back and fourth between the shyguy pipe and the pipe that you're standing on killing the shyguys coming out the pipe.
Be careful, because if a shyguy is standing too close to a pipe and the shell hits it, the shell and the shyguy will be destroyed.