In the military world I know, there are some SOPs. If you plan to take part to an exercise on an known airbase, you have to find the “domestics” documentation and study it carefully (Nellis for Red Falg is an example).
If you divert on a (big) airbase and you are not familiar with the taxing circuit, you can ask for help (radio) or even request a “follow me” car in some cases (handling or base ops duty) … But in any cases (except some extreme emergencies where you could land on an unscheduled airfield), you have to take all the needed airfield plates in flight, and be able to taxi by following ground instructions. Worse case, vacate the taxiway and shut down the engine … then wait to be towed to the apron 😉 LOL
To cross a runway, you always need a clearance. Either by radio, or visual sings (the “Silent day” at red flag where all a/c taxi and takeoff without any radio contacts.