HWD,
A run and break is typically carried out this way:
A long, straight approach down final, sometimes from a few miles out, usually at high speed but can be at any altitude up to circuit height.
From the midpoint of the runway, the pilot will execute a 180 degree turn to put himself onto a midfield downwind to start a curved approach onto short final to land. Sometimes the pilot will come in low and pull up to circuit height during the turn but it can vary from that to a run AT circuit hieght and a horizontal turn onto downwind. This will sometimes be a shallow turn or a steep turn, climbing to circuit height, or horizontal at circuit height. It usually puts the pilot on a close-in downwind position at approximately midfield, so the curcuit flown is much tighter than your average circuit.
That's for a solo pilot. For a formation, the same applies but each aircraft will peel off with a set separation, usually with the first one peeling off over the approach numbers and then each subsequent aircraft on a 5 second delay. This ends up with a group of aircraft all in stream on downwind, now under their own navigation and setting themselves up for individual landings. Sometimes they'll fly extended downwinds to get the timing of the landings right.
So, having said all that, the places to look when you hear a call for a run and break are starting along the final approach out to a couple of miles, usually low (say 500 ft QFE). The run in will often be fast. Then look along the runway for aircraft executing their turns up (or across) to a close-in downwind. Then look for curved final approaches sometimes starting the decent from abeam the numbers. Rarely will the pilots fly a standard square curcuit with a run and break, so their time from downwind to final will be pretty short.
If it's a formation, the leader will usually announce how many aircraft are in the formation when they approach. Try to remember how many to expect and count them off when you see them. That way you'll know if you'll know you've got them all in sight.
Most run and breaks I've seen have been executed with due regard for local traffic patterns and other traffic in the circuit, but I'm sure there are plenty of examples where that hasn't been the case.
A run and break will often be announced by a radio call something along the lines of "G-XXXX turning Initial for a Run and Break, runway 26, 30 seconds(or X miles) to run" or something close to that.
I hope that answers the question. If you want to see properly executed run and breaks, spend a couple of hours at Lakenheath's Spotters' Corner. The Eagle drivers know how to do it!
If you've got any other questions, ask and I'll try to answer them.
Cheers,
Pitts2112