1) accept that housing is a consumable. The exception is nokon, but then you still have to replace the liner.
2) buy stainless inners as a minimum, the teflon/polymer coated ones are an improvement on just stainless. There’s also the cord cables rather than wire, but they’re silly money.
Shimano SP41 outers come pre-greased (another good reason to just buy it and bin once shifting deteriorates).
The only other thing’s I’ve found to improve shifting are R&R cable magic which seems to work well with middleburn cable oilers, or dipping cables in putoline wax (I’ve taken over TJ’s role of being the resident putoline evangelist)