Help and advice

Hi I am a step mam to a 7 year old boy who has been diagnosed as been autistic,  i have never had any involvement with children so am trying to learn all the time but i feel i do struggle to try and bond without over stimulating him to a point where he has a melt down, i just would like any advice on how to recognise potential triggers and what to do when he has a melt down and how do you know if it is just been naughty or it is something caused by his autism.

One day this week in particular he was been really naughty although i do not know if it was a melt downas  he does not use words to express himself, i was shouting at him to stop doing it but to my mind it was making him worse.  The only way that i found that helped is i distracted him and starting playing with a football but am not sure if this is the right technique as would this be perceived as rewarding bad bahaviour or a good distracting technique?  any advice would be most welcome.