Thoughts on Lookout
Several posters have noted the relaitive difficulty of spotting a static (ie real risk of collision exists) target as against one where there is relative movement across the canopy (and low/no risk of collision)
However gliders rarely fly in straight lines and very few GA aircraft are required to.
To avoid the dots staying static before your eyes, first, move your head: a moving-head scan (IMHO) picks up more than a long stare. Second, manoever the aircraft. Pre aeros/spins checks recognise the need for 'clearing turns' to get a good view in blind spots above/below/behind; well why not do some in normal flight? They don't have to be knife-edge manoevres to panic the pax, just avoid sustained stright-line flight - every change of heading (with its instinctive associated extra lookout) increases chances to acquiring a target.
Not rocket science, but every little helps
'Simples!'
BTW, I question the contributor who reckons greatest risk of collision is in the circuit: with everyone going the same direction, with the same intention and on the same frequency, all these factors reduce collision risk.
My top candidate for a collision black spot is a recognisable landmark, suitable for use as a glider or GA cross country turning point, especially if it also marks a choke point between areas of controlled airspace. The combination of the controlled areas squeezing non-IFR traffic into smaller spaces and the landmark attracting them multiplies the dots on the canopy amazingly!