As somebody who works charter trains on the national network as a Guard with the exception of one occasion I've gone out and covered the routes and learned them the same as I do for my day to day TOC. I look at the stations along the route for method of dispatch, dispatch staff, any off indicators, banner repeaters, any hazards that are location unique, along the route between the stations I'll look at the direction of the lines especially as in many places it can change repeatedly, line names, controlling signalboxes, junctions and where they lead to, electrification, method of signalling, special and local instructions and anything else I feel I need to know to safely work a train.
One of the most interesting things I suppose is that the majority of charter trains I've worked are self dispatch in the majority of locations however some TOCs seem to have mandatory dispatch so whilst on my paperwork I'm self dispatch everywhere, I always liaise with any platform staff present to determine their level of involvement, be that anything from observation, operating TRTS, giving the tip, assisted dispatch (50/50 checking doors with me) to full dispatch. I dispatched a charter at Stockport earlier this year and had 3 dispatchers do full dispatch for me and even operate the RA indicator!
I have access to route maps and videos to assist with route learning covering the majority of the country, backed up by the electronic sectional appendix, and notices for the network emailed to me.
I tend to find I'm more hyperaware (cautious?) when I'm working a charter service primarily due to the lesser familiarity with the locations than somewhere I've dispatched from 1,000s of times but also because of the slam doors.
