The London Buses Historic site seems to have a lot of 1966 fare charts - I've tried a couple of other routes at random and not found a 1969 one.
There is a reference in Ken Glazier's book 'London Buses in the 1960s' to fares in 1969 being 6 pence, 1 shilling, or 1/6 - this suggests that the 8 penny fare in 1966 might have increased to a shilling by 1969, so a fare of a shilling would not be wildly inaccurate.
At that time, travelcards / bus passes (broadly speaking) did not exist, and London buses then as now did not do return tickets.
At the risk of stating the absolute obvious, the passenger in 1969 would have got on the bus (probably at a bus stop, but possibly at traffic lights or in slow traffic), gone and sat down, then the conductor would have come round for their fare. I have seen a couple of examples on the telly where passengers have either paid the conductor on the platform on boarding (this did occasionally happen on lightly loaded journeys, but unlikely on a journey from Piccadilly Circus) or in one case, leaning across the bonnet to pay the driver...
The conductor would have issued the ticket with a 'Gibson' ticket machine - short video of conductors in training
here.
Smoking was allowed on the top deck of double deck buses then.
If it's of any possible use, in 1969, the conductor could have been a woman (women conductors were taken on during the two wars, but after 1945 were allowed to keep their jobs, and women conductors continued to be recruited) and / or from an ethnic minority - London Transport was recruiting in the West Indies from the late 1950s, and many migrants to London from Ireland and the Commonwealth worked on the buses. (From the location of garages that worked routes 12 and 53, a West Indian is statistically more likely than an Asian.) The driver also may have been from an ethnic minority, but would not - until 1974 - have been a woman.