I fly from a controlled field, where we have a VFR training circuit at 500 feet (with a very displaced threshold) and the regular circuit is at 1000 and 1500 feet, depending on the arrival route. All three circuits are very tight (downwind to final is one 20/30 deg turn, no base being flown as such) due to noise considerations. Obviously there are no obstacles that violate rule 5 on the training circuit... Having done a lot of these 500 feet circuits really helps if you get caught by the weather. Particularly the day the ATIS reported 1200 few, 1500 overcast, but in reality it was 800 broken. Tail between the legs, low level circuit and back to the coffee... I wrote that one down as "character building" in my logbook.
As others have said, remain in VMC, fly a tight circuit keeping the runway in sight at all times, and be prepared for the fact that everything happens much faster. I try to get as much done on downwind as I can, only needing the last stage of flaps to lose the last five knots or so to Vref on final. Days like that, the circuit is never busy so if you fly it a little slower (2 stage flaps, 70 knots on downwind) than normal, you're not holding up anyone else anyway.
As for the precautionary landing - we did a mock one on my PPL course. You don't actually have to *land* on precautionary landing training. The most important aspect is that you overfly and inspect the potential landing area from an increasingly lower altitude for increasingly smaller obstacles:
- First pass at 500 feet or so to look for power lines, trees and such
- Second pass at 100 feet or so to look for cattle and such
- Third pass at 20 feet or so to look for stones, ruts and such
All these passes are done (in a PA-28) with 1-2 stage flaps and 70-75 knots or so. A speed which is high enough above the stall to allow 30 deg turns, but slow enough that you've got time for the inspection.
- The fourth pass is a landing. We didn't do this, despite the fact that we did the whole sequence at an (uncontrolled) airfield. But you can train the same thing above a farmers field as long as you don't violate rule 5.
Between passes you climb to a sensible altitude, but not necessarily a regular circuit altitude. After all - one of the reasons for a precautionary landing is inclement weather and no suitable diversion close by. Thus, you might not have the luxury of having a normal circuit altitude below the cloudbase.
Best approach, as far as I'm concerned, it just to learn how to be flexible with your circuits. Learn how to do them at 500 feet, learn how to do them at 1500 feet (with a kamikaze turn from downwind to final without gaining speed), learn how to do them fast (90 knots or more) and slow (70 knots or less), tight (500 meter or less from the runway centerline) and wide (where the base leg is longer than downwind. Take a look at the EHTX summer weekend approach procedures for an example). Learn how to do an orbit on downwind for separation with a 737 on final. Learn how to do direct base or direct final entries. Learn to fly the whole circuit with 2 stage flaps, at the bottom or even the wrong side of the power curve, and learn how to do flapless landings and short-field landings. Learn how to approach and hold off with the power on, floating above the runway just above the stall speed, in ground effect, with a crosswind, in case the tower asks you to "expedite vacating, traffic is a 737 on short final behind you" and the first (high speed) exit is still a kilometer away. With all these tricks in your arsenal you should be able to adjust your circuit safely to all sorts of conditions, regardless of whether they are weather-related, traffic-related or otherwise.
And mind the classical turn-to-final stall... Even in inclement weather, it's better to throw away the approach if you're likely to get into the stall there, than to press on and stall/spin in a situation where you have no height to recover.