What are the rules for "see and be seen" when you suspect a potential conflict in class G airspace? The airfield I learned to fly helicopters at is in uncontrolled airspace and has an air/ground radio service only.  It has a main runway, 07/25 and a secondary runway only used in high x-winds, 13/31.  

 

All fixed wing circuits are to the North so fixed wings will fly right hand circuits when operating Westerly and left hand circuits when operating on the Easterlies.  Helicopter circuits are always to the South so the reverse is true.  This works well and keeps fixed wing traffic separated from helicopters.

Therefore, there is no "dead side" since the Southern leg is the downwind for rotary and the Northern leg is downwind for fixed wing.

Once, when preparing for take off from runway 25, I heard a call from a fixed wing announcing they were about 7 miles to the East and would "join dead side".  The A/G operator reminded the pilot, who clearly wasn't one for reading the relevant publications, that there is no dead side and advised them to make a standard overhead join.  We were operating to the West so my circuit would be left hand to the South.

The next call I heard from them was on the downwind leg when the pilot announced "descending dead side".  The operator reminded them that there was no dead side and more insistently instructed an overhead join.

I am now at 1,000 feet on my downwind with an aircraft I suspect is in front of me heading towards me and descending!  Referring to the plate, I am heading roughly East to the South of the road marked "A303" at the bottom of the plate.

I took 3 actions;  I made a position call of "downwind South", increased my height to 1,200 (I figured they were likely to have joined at 1,000 feet) and switched on the landing light.

I can't find any rules of the air or rules of thumb to help in this situation.  Are there any?  Is there anything else I should have done to help to avoid a conflict?

I never did see the other aircraft and I knew from the pilots actions and their lousy use of the radio that they were inexperienced or incompetent and I didn't go looking for them when I was back on the ground to "share a little wisdom" with them.
In the USA, RW aircraft are supposed to avoid the flow of FW traffic and FW traffic have the right of way for landing. 

So I would have descended to 500ft instead of climbing. Slight differences in altimeters make 1,200 and 1,000ft too close for comfort. But  500ft AGL (noise abatement be damned in a safety situation) is a perfectly acceptable altitude in a heli. 

Also, I would have adjusted my downwind so that I was fairly close to the runway where airplanes are rarely found. 

So now I have both vertical and horizontal separation, and I am in a continuous position to land, at my convenience.