Plant the seeds in high-drainage soil. Whether you bought seeds or harvested them from an existent cactus, you'll want to plant them in clean, shallow containers filled with suitable soil. Moisten the soil thoroughly before planting but do not allow any standing water to remain. Next, spread the seeds across the top of the soil (don't bury them). Finally, lightly cover the seeds with a very thin layer of soil or sand. Cactus seeds only have a small amount of stored energy and if planted too deeply will not reach the surface before they run out.
It's important to use a high-drainage soil for planting your cactus,especially if you're dealing with desert varieties. Since desert cacti aren't used to receiving high amounts of water in their natural habitat, they can be susceptible to root diseases if the moisture in the soil is not allowed to drain. Try using a high-quality potting mix with a high pumice or granite content for exceptional drainage.[3]
If the soil you use for planting hasn't been pasteurized (it should say whether or not on the packaging), you may want to consider heating it in the oven at 300o F (about 150o C) for half an hour. This kills any pests or pathogens in the soil.