We had many students from India and the main reason why their speech was difficult to understand is that they spoke very quickly. This fact leads to two issues when they speak English:
They clip long vowels and diphthongs and do not lean on them. Failure to create long vowels and diphthongs makes speech difficult to understand
They fail to make appropriate grammatical pauses to separate their ideas. As a result, what they said becomes difficult to absorb.
As well as that, because many English sounds do not exist in India, Indian speakers of English have difficulties pronouncing:
The /w/ sound as in “win”, they substitute it with /v/ as in “vet”
/θ/ and /ð/ sound as in “think” and “that”. They substitute with /t/ and /d/ sounds as in “tick” and “Dad”
/r/ as in “rat”, they vibrate the tip of the tongue and as a result, it does not sound English. In English Standard pronunciation, when pronouncing the /r/ sound the tongue is curled and kept still.
Our first recommendation would be to practise long and short vowels and their comparisons first, and after that practise all diphthongs with the apps Elocution Lessons, Get Rid of your Accent UK1, and Business English Speech. The same apps are also available on Google Play. They are based on bestselling books in the series Get Rid of your Accent and have audio and recording buttons. Work with these apps together with the accompanying video course Get Rid of your Accent Part 1
Once all the sounds are sorted, we suggest working on sentence stress and intonation with the Fluent English Speech app and the accompanying video course Get rid of your Accent Part 2.
The real game changer would be to slow down the pace of the speech with the app Power, Pitch, Pace, Pause.