The way I see it is that I give an inbound broadcast about 6 minutes out so there is time to sort separation. I also give a call joining downwind, maybe mid downwind if I join over the top, and a call turning base. This one is the biggie coz potential conflicts get serious now. Also coz I'm turning, the aircraft is as easy to spot as it will ever be.
You don't need to say much on these calls, just place & position with ETA as well for the inbound.