Hello,
You have been given good advice already....forgive me if some of this is repetition, but here's what I would do:
1) Make sure you have both genders
The bottom fin on females is shaped like a fan....the bottom fin on males is pointy and well, you know....
The ideal balance is 2 or 3 females for each male. (The males can be quite agressive)
2) As has already been suggested...you need LOTS of plant cover...both near the gravel and some floating plants are good too...(floating but anchored to something).
3) Increase your temp slightly...ideal for breeding platys is around 78 degrees or a bit higher.
4) I don't recommend separating the mom or the babies from the tank...they do best when left where they are. However, expect some fry to be munched by the adult platies and/or the danios. (thus the importance of some THICK plant coverage)
5) If you can move the danios to a different tank, that would be best....the adult platies will learn not to eat the fry with time....not sure why but it's true. I have days old fry in my tank that swim freely with no fear of being munched. But my fish are used to seeing little fry...
6) A female may have upwards of 30 fry at one time and they are live bearers (no eggs in tank).
7) The female will get very round and you will see a dark spot on her underbelly near her bottom fin. Once you see these signs, wait about 2 weeks or so and you should see little ones. I have tricks for feeding them, so feel free to PM me when you're at that point.
8) Good luck!