In order to reach the other side of the first gap in this section safely, you must run with super speed and jump before you hit the block.
It'll take some practice to stop on the one block column at the end of this section from a jump, but it may be worth it to collect the Starman from above. Choosing not to get the Starman creates an opportunity for a 1-up: capsize the first Koopa Troopa and kick it to the right.
In Vs. Super Mario Bros., watch out for an extra bottomless pit after the first pipe, which includes a pipe.
Be very careful on the final staircase. Jump on the high block to avoid crashing into the Goombas that drop down.
In Vs. Super Mario Bros., also be careful where the three blocks are. There is an empty space instead of a middle so your best bet will be you'll need a running start to cross. After that, there is no elevated block to protect you from the goombas.
As long as the ceiling is two spaces high above your hero's head where he is supposed to land, you can guarantee a safe landing. However, there are some areas where the ceiling clearance is too low to guarantee it. If you are regular sized, you will be safe. If you are super sized, you will need to land a proper way, or you will likely fall into the pit.
It is easier to land backwards than forwards. One solution is to dash before you jump or fall, and then land backwards. Stop too soon, and you might not land.
After you pummel the Koopa at the top in the very beginning, you can kick the shell to the right and follow it as it plows through the enemies below. If you don't lose sight of it, you'll earn a 1-Up.
You'll need good distance in order to clear the large gap at the end of this section. Run with super speed and jump when the Fire-Bar is on the right side.
Find a valuable Power-Up in a hidden block above the passage entrance. If you are Mario, you can only pick up a Mushroom.
Although this level is a possible source of infinite lives, you have to sacrifice a life to go back to the beginning, so trying for infinite lives might not be worth the trouble here, particularly in the original game.
Drop down to the floor just before you reach the passage in this section. You'll avoid most of the heat from the Fire-Bars and the Fireballs above. Make sure to dash over the small pits.
Balls of fire known as Podoboos in the Mushroom Kingdom fly up from the pits. Wait for them to sink back down, then jump.
If you're confident that you can hold off Bowser's attack, you'll find a 10-Coin Block in the left brick wall over the bridge. Collect it at your own risk.
Wait for a big bonus
If you grab the axe at the same time that the timer ticks down to zero, you'll earn a time bonus for 999 clicks of the clock; 50,000 points! Be careful, though — it takes a well timed jump, and remember that points don't give you extra lives.