New cable housing from Jagwire, for example, have a Teflon liner that is quite effective. They also recommend not lubing it because that can cause it to accumulate sludge. New cables and housing can make a huge difference.

Be aware that modern bikes with indexing shifter use different housing for brakes and derailleurs. The derailleur housing has multiple steel coils running more longitudinal than the traditional single coil. It makes the housing less compressible, necessary for accurate shifting, but it also makes it WAAAY too stiff if you aren't running index shifting. If you go to your LBS and ask for housing the person you speak to may try to give you derailleur housing, and possibly doesn't even know that friction shifting still exists. Also LBS youngsters tend to think all bikes have internal routing for rear brakes and aero levers, so they never give you enough for a complete cable overhaul.