Since we have yet to lose personnel onboard the ISS due to starvation, I assume that space agencies have got a good handle on the mechanics for a rendezvous in low earth orbit.
What would be the (added) difficulty in organising a rendezvous between spacecraft in orbit around other planets? Are distance or the knowledge about the planet in question factors in the complexity of these maneuvers?
It is a bit trickier due to the reduced availability and/or accuracy of terrestrial navigation aids such as the Near Earth Network and GPS. But certainly possible though it hasn't yet been demonstrated outside of Apollo. Rendezvous around Mars would rely on a combination of orbit solutions from DSN ranging with optical and cooperative radar measurements on board each spacecraft.
The MRO observations of MSL and Phoenix under parachute and IIRC of Mars Express show that ~1 km position knowledge and extremely accurate pointing are possible even with noncooperative targets.
If unmanned, the initial launch trajectory would be preprogrammed based on earth's best estimate of the target spacecraft's orbit. Autonomous navigation would take place for the latter part of the rendezvous using the seeker spacecraft's onboard sensors and computers. This has already been demonstrated in earth orbit.
The point of going to Mars is to use its resources on the ground. Otherwise one could just stay in empty space, building a space station. An automated fuel factory (extracting CO2 from the atmosphere) will have to land on Mars well before the crew. And with it a power plant. And most practically the ascent vehicle which its purpose is to fuel.
So there doesn't remain much to put in a waiting orbit. Maybe the habitat, but if it and the crewed spaceship doesn't land near the ascent vehicle, they have a serious problem. Orbiting Mars doesn't give you many options anyway, until a lot of infrastructure has been constructed there. It is safer to make sure that all preplaced assets are on site and working before even launching the crew from Earth. The landers and ascent vehicles should be minimized, like elevators. A return-to-Earth spaceship, or even a Mars cycler, might be a very good idea for the ascent vehicle to dock with in near Martian space.
I'm sure someone more knowledgable here will explain how it is a huge waste of fuel to enter Mars orbit before landing, instead of just crashing down through the atmosphere on arrival.
