Firstly, you will need to condition the pair of Zebra danios with the best meals possible so they can quickly hold up against the pressures of reproduction. Consider feeding them fresh or frozen shrimp or white worms at least twice a day for one week before they can start mating.
A reproduction reservoir should be set up for the breeding pair. This reservoir should be narrow and must be "cycled" using some mature Zebra danios. Consider moving the grownups to the primary reservoir once the process of reproduction begins. The reproduction reservoir should also contain huge glass beads as the substrate. This rough content gives the egg a lot of gap areas to fall into after they are set. This way, the mother and father cannot get to the egg to eat them before you even recognise they have been laid. Some individuals like to use plastic material reproduction aquariums that fit well within your tank, but this can be unpleasant and heavy, because you still have to keep the mother and father away from the fry until they are big enough.
Consider putting several Zebra danios into the reproduction reservoir. Within some time, you should observe the breeding action. Let some time pass and then take out all the grownups and put them back to the primary reservoir.
The egg should hatch out in a day or so. The fry look like little dark collections adhering to the edges of the reservoir. If you don't see any fry after a short time, you can try again after your couples have been relaxed.
Start providing the fry with dry meals after they are at least a week old. The meals should be perfectly ground flakes or other meals designed especially for fry.