For writing, only two rules.
1. Look for character on screen and press indicated key.
2. If character not predicted, press Next List button. (Select/OK btn)
Be familiar to writing in Indian languages : matras, yuktakshars, bindis etc.
अंतर्राष्ट्रीय =
अ + ं + त + र + ् + र + ा + ष + ् + ट + ् + र + ी + य