I have been part of the RCIA team in my parish for about 20+ years. Normally we go over this during the Holy Saturday morning retreat, but I do not know what your parish does.
As to how to receive Communion on the tongue, a few pointers:
- Stick your tongue out. I don’t mean put the tip of the tongue out, I mean stick it out. No matter whether you receive from a priest, a deacon or an EMHC, they all have the same problem putting the Host on your tongue if you only stick the tip out.
When I was an altar server in the 1950’s, more than once I heard the priest say “Stick your tongue out”. The number one cause of the communicant losing the Host was that they did not stick their tongue out far enough to get the whole Host on the tongue; sticking part of it out leaves the Host liable to fall off.
2 - Open your mouth and keep it open as you take the tongue and Host back into your mouth. This is the second cause of losing the Host. That is because if you do not keep your mouth open, the Host is likely to hit the tip of your upper teeth and be flicked off. It may seem awkward, but it is more awkward to receive the Eucharist in a Byzantine Rite where the Eucharist is delivered by a small spoon.
It may seem awkward at first, but if you simply follow the above, you will receive without any problem.