How little do you know?
Planning ahead involves running a series of strings or pull-tapes through the conduit. With each cable you pull through to a destination, you pull a new string along with it. You learn that kind of stuff when your runs start exceeding the length of a fish tape. The technique can easily be applied to even the shortest of runs and it can be pre-routed through arbitrary junctions in the conduit. If you're careful, you can even establish new branches by sectioning the conduit and attaching to a string from another branch.
I have a run at work that is 790' long at I've put two 25 pair CAT3 cables and a duplex fiber in it. The conduit was originally buried with a single length of synthetic twine inside. It is strung for another run when I upgrade the fiber for Gigabit networking (I plan on leaving the old fiber in place). In my experience, pulling a string works a lot easier than pushing a fish tape.