Well, that has to do with the impedance of the cartridge on your record player. Unfortunately there are lots of cartridges out there with different impedances so if you want to build your own, find out the exact impedance your cartridge has.
With that information, you can build your pre-amp to match that exact impedance and you'll also have to implement the RIAA equalization to match. If at the end of the build, the music will sound flat and bland, then there is a mismatch between your cartridgew and the pre-amp.
One very good source of information would be Douglas Self's books. I think "Self on Audio", "Small Signal Audio Design" and "Electronics for Vinyl" might get you started. I'd personally start with the Small Signal Audio Design one.
Of course, he's not the only source of info out there, but he has, I think, the most "bang per buck" in those books.