How can I join in with football without making a fool of myself?

At school, all my friends play Aussie Rules, and I usually avoid participating because the last time I tried to tackle someone I accidently knocked them out (oops). How can I play better and not feel so self-concious about joining in?How can I join in with football without making a fool of myself?
wow ummm it was probably your way of tackling you need to wrap around their body and lay them down gently if your strong... and maybe play a position like safety or Corner back where your focusing on picking off the pass instead of cracking them (maybe not safety because if they catch it and they come towards the end zone you might have to hit him)