Steps : (Will be described in detail in tweet threads)
1 -Taking Backup of iphone(for existing users)/New iphone
2 -Preparing the android & iphone for transfer
3 -Transfer & Restore process
4 -Restoring the old phone backup data(Not Whatsapp) with new whatsapp transferred data
1 : BACKUP OF IPHONE
-requires a mac/pc with itunes OR icloud backup if you can pay for extra storage
-install itunes for your system and connect your iphone>go to the phone icon>take manual/automatic backup
-if confused,refer a youtube video for this, it's self explanatory.