In order to successfully ensure that your discus fish produce next generation of fry, first you must ensure that you obtain a breeding pair. Gender of the discus fish can be difficult to determine and basically getting a right pair is often a mix and trial process which is done by having at least five or more of the fish together in the same tank. If possible, you can also try by having multiple discus variety so that there are high chances for you to obtain a cross and mixed breed. My advice on this process is that do not try to force them together to pair up because these things must occur naturally and you really can’t predict the outcome.
Once you have successfully obtain your right breeding pair and they are ready to mate, you should start transferring the rest of the fish to another aquarium. This is to avoid having undesired aggressive action, which could result in the other fish getting injured because your breeding pair will try to protect a spawning spot it has chosen. This includes the pleco catfish, which you put in earlier to play a role to clean up the tank. Fish breeders normally put an inverted flower pot while others that I know will just leave a barren spot for the breeding pair either way, both methods are still considered good enough.
During this critical period before the female start to lay eggs, it is imperative that the water conditions should be clean and water parameters tightly controlled in order to avoid undesirable effect such as ammonia or nitrite buildup. Waste in the tank should be immediately removed and try to conduct partial water change once every 2 days. Water temperature should also be maintained close the 88 degrees Fahrenheit level and if you do not mind investing some money on water test kits that would be the best option. Remember, you can’t risk having an unhealthy fish or else your effort will go to waste. (Learn about ideal tank condition for discus care)
On the nutrition side, your discus fish should be supplied with fresh live foods and in order to avoid introducing unwanted disease which you affect the breeding process, only source your supply from reputable suppliers. There are even some commercially prepared fish flakes which are tailor-made specially for discus breeding pair and if you managed to grab hold of these, it would definitely help to stimulate and ensure they will spawn.