Temp 28 to 30'C
PH 6.4 to 7.5 ( a stable Ph is the priority)
GH and KH 3' to 11'
The main thing with discus is to keep the water as clean and as stable as possible, that means no nitrite or ammonia, keep phosphate and nitrite to a min (the plants will help with this) and temp and ph as stable as poss ( as discus don't tolerate big fluxuations in water parameters and quality)
Discus are shoaling fish so keep in groups of six to eight no less then 4 unless you are buying an adult pair.
Tank size as a rule of thumb one adult discus per 10gal, so a minimum size tank is 66 gal, which gives some room for some small dither fish such as tetras.
If its your first time in keeping discus i recomend having a bare bottom tank, with bogwood and some plants in terracotta or plastic pots (such as amazon swords, java ferns, anbuias hygrophilia polysperma etc), as it will be easy to keep the water clean until you get the hang.
The main thing is to create light and dark areas, shelter and open areas so they have a chose and feel safe.
I use bogwood on sucker to create over hangs.
If you have to ave a substrate, silver sand, quarts gravel, anything that is inert (wont change the PH)
Maintaining your tank, i would recommend no less than 30% water changes weekly (more is better), during which you can do your gravel cleans.
When feeding always remove uneaten food as it can quickly break down in warmer waters polluting the tank
Remember the more often you change it the more stable the PH will be.
Water, check the quality of your tap water if you intend to use it, as ph and other water parameters can fluxuate.
also tap water can sometimes contain high levels of Phosphate and heavy metals which will weaken there immune systems and open them up to secondary infections that might lead to death long term.
Personally i recomend r/o water as it is far easier to control water parameter.
The main thing is to match the PH and temp of the water before adding it, by using products such as seachem equilibrium or kent r/o right for the GH and bicarb of soda for the KH, or to raise the PH the more you add ( experiment before adding make sure)
Foods its best to feed discus little and often as this is the way there would feeding the wild and also this way you can make sure all food is eaten, and none is left over to pollute the water.
Bloodworm, brineshrimp, mlysis (river shrimp) quality dry foods and special beefheart mixes for growth (its a good food to feed young fish to promote growth but will involve extra water changes as it soon lowers the PH).