This level features a large number of Bob-ombs. They will eventually explode after being hit, which is both potentially helpful and dangerous. Also remember that you can pick them up and throw them while they're ignited.
Start the level by jumping into the second ? block you see to get a fire flower. Avoid the falling bob-ombs and jump over the pokey ahead. Soon, you'll see hills with layers of dirt on top. An explosion on one of these will cause coins to erupt, making it worth throwing defeated bob-ombs there. Over one of the hills, you'll see two pokeys on the same platform. The ? block to the right contains another fire flower. Further right you'll see cannons shooting out bob-ombs. Use this live ammunition to blow a hole in the barriers separating you from the first star coin.
Immediately after the midpoint flag, hit the ? block for another fire flower. Immediately ahead, you'll see a sand pit with coins. Sink down it to reach a hidden area. In the area, use the bob-ombs that shoot out of the cannon to break open the top of the hill. This will reveal a 1-Up, a bunch of coins, and the second star coin. If you need it, the nearby ? block contains a fire flower. Once you're done, head up via the green pipe.
Back on the surface, you'll see a floating platform on your left. Hitting the middle block reveals two roulette blocks on either side, each of which can release up to 50 coins. Beware the bob-ombs shot out of the cannon though. To the right, you'll see two distant cannons shooting towards each other. Up and in between them is the third and final star coin. The key to getting it is to jump on one of the bob-ombs they fire while midair to get the extra boost necessary.
The final part of the level contains a Red Ring. Collecting its coins will grant a 1-Up. Then, there will be a section with three cannons shooting towards the right. Jump on top of their shots to reach the top of the flagpole.