Now for the next post about Radio Procedures. Again, this mostly applies to people operating with ATC, but I'll give info for uncontrolled once I fly to one :P
*When making contact with Ground Control before taxiing, make sure you request taxi to the active for Circuits.*
There are really only two calls to be made while flying circuits. The first occurs when you're about halfway along in the downwind leg: "Random Tower, Alpha Bravo Charlie is left downwind Runway 32 for touch-and-go." You can change this according to your situation.
The tower will then either tell you that you are number one and are cleared to land, in which case you will acknowledge with your callsign: "Alpha Bravo Charlie"
More likely, the tower will advise you your number in the circuit and will give the location of other traffic. If you positively identify the aircraft as the controller is talking, you reply: "Alpha Bravo Charlie is with the traffic"
If you have to look for the traffic, you reply: "Alpha Bravo Charlie is looking for traffic"
That's about all you need to know for radio procedures in the circuit at controlled airports. For some great examples of radio procedures, check this out:
This is a recording of the radio chatter at CYKF (Waterloo International), June 26th, between 1330Z and 1400Z, from LiveATC. I am the one flying CVX, along with my instructor. I make initial contact with the Tower at about 1:50 on the clip.