A guide to completing World 3-1 in Super Mario Bros 1 for the Nintendo Entertainment System.
Explore World 3-1
Go to the right and be careful of the two green Paratroopas that bounce toward you. The rightmost ?-mark block contains a Mushroom or Flower.
To the right, there are two pipes with Piranha Plants coming out. You can go down the rightmost pipe, but if you're regular-sized Mario, you won't be able to get all the coins in the secret area. If you're Super Mario or Fire Mario, don't break all the bricks under the coins. Just break the leftmost blocks and rightmost blocks, then jump to get all the coins. There is also a Flower in one of the bricks on the left side.
If you decide not to go down the pipe at all, you'll just encounter some enemies and a brick.
Whichever you choose, when you go right from the fourth pipe, you find some stairs up to a bridge over water. If you collected all the coins in World 2-3 without dying, or if you warped to 3-1 via Warp Zone, there will be a hidden brick above the right side of the bridge. If you stand to the right of the rightmost cloud over the bridge, then jump, you'll hit the secret brick. It contains a 1UP Mushroom.
Go to the right and hit the leftmost brick to get a Starman. Touch it to become temporarily invincible, then quickly jump over the pipe on the right and you will encounter the Hammer Bros. They are tall turtles that throw hammers at you. If your Starman is still active, run into both Bro to defeat them. Or you can hit the brick that a Bro is standing on to defeat it. You can try jumping on top of a Bro, but you have to be careful not to do so when he is throwing a hammer.
In the platforms where the Hammer Bros. were, the rightmost ?-mark block contains a Mushroom or Fire Flower.
To the right, there is a spring, but if you want to climb up a vine to get a bunch of coins, ignore the spring and make a running jump to try to get between the two brick platforms to the right of the spring. If you make it, hit the rightmost brick to make a vine come out. If you don't feel like climbing the vine, skip to the next paragraph. If you want to climb the vine, touch it and press up to go up. Then just jump onto the platform that looks like pearls, and it will move to the right. Jump to try to get as many coins as you can. You'll need to jump on some cloud platforms along the way to try to reach them all. Toward the end, there are some clouds with small gaps between them, and if you hold the B button, you can run across and you'll automatically "jump" over the gaps. From there, try to jump down through the three coins past the edge of the lower clouds.
If you didn't go up the vine, go to the right to go up the stairs, and make sure not to fall straight down after the last step. To the right, the bottom-right ?-mark block contains a Mushroom or Flower.
Go to the right and hit the second brick from the left to get some coins. Then jump up the blocks on the right, being careful not to fall off into the pit on the right.
After you get past the pit, you find stairs on the right. This is where you can perform "Turtle Tipping", a famous trick to get infinite extra lives. To perform this trick, ignore the first Koopa Troopa and let it walk down the stairs. Then jump on the second Koopa Troopa, but don't let its shell get away. Instead, jump on top of the left side of the shell so it bumps into the stair on the right, in such a way that you will jump on the shell again as soon as it starts coming back. It can be tricky, but if you position yourself just right, you can let go of the controls and you will keep jumping on the shell over and over. You will start getting 1UPs after you have bounced on it several times. This happens because if you defeat a bunch of enemies in a short time, such as by kicking a shell through them, you get more and more points for each enemy, and eventually instead of points you get 1UPs.
When you're done, go up the stairs, then run and jump to the right to reach the goal pole. You'll continue on to World 3-2.