I think this whole topic should be broken down into parts:
Firstly, there are various things you can do to reduce the risk of collision that are unrelated to detecting the other aircraft. In short these "things" all revolve around avoiding areas with a high density of traffic - as IO540 says, fly high for example. I gave in my first post a list of other things that will help.
Secondly, developing a scan technique to give you the best chance of spotting another aircraft. However, kid yourself not, if you take the trouble to read all the research, our eyes are really not up to the job. You will get quite a different impression from this and other forum - all I can say is those who punt this are irresponsible and clearly havent read the research.
Thirdly, we can use technology to help. Technology inevitably is the last line of defence. The kids on the chopping block are PCAS, TAS, FLARM and transponders. FLARM is the odd one out because it is only gliders that really use FLARM and even then I personally suspect the uptake is no where near as large as they would have you believe. For that reason, transponders and PCAS or TAS IS the only game in town at the momement, if you have to select one or the other. The alternative is to have both.