It's a combination of things not any one thing.
1) keep the blade dry. In other words don't store it wet. SS doesn't rust, but it pits so if you store it wet it will pit. The thin edge (sharp edge) pits the easiest and needs to be stored so that it faces up so that any water remaining drains away from the edge.
2) Strop it. That's running it backwards across a surface multiple times to "perfect" the blade. You aren't sharpening it, you are getting rid of minor imperfections. Barbers strop their blades on that long leather strop attached to the barber chair. It seems most people here use their forearm. I strop mine before and after each shave. It only takes a few seconds.
The plastic guides don't allow you to strop it on a hard, flat surface. I use my arm and I also occasionally use the slightly curved surface of the glass bricks in my shower.
3) Shave first. Sounds odd, but it works. I use an electric razor first then finish with a manual razor.
You don't need to use the electric razor till you get razor burn, you are only mowing it down to a shorter level and getting the places that a manual razor isn't the best at, like around your mouth. This way you don't keep shaving your lip off.
You know how it hurts the first time you shave after not shaving for a complete race weekend? That cause the longer the beard is the rougher the shave. What you are doing is quickly mowing it down with the electric razor to a level that makes your manual shave more comfortable and gives you less pulling.
Using 2 razors means neither razor has to work very hard. You don't have to run the electric razor over and over the same spot trying to get the last little bit of stubble off and you don't have to put nearly the work into the manual blade.
Your electric razor doesn't even have to be that sharp. My electric razor is over 5 years old and I've only replaced the blades in it once.
I used to get only 5-6 months on a blade, but when I added the stropping my time went to a year.
My beard is what would be known as a medium beard, but my son-n-law has a beard that gives him an11 a.m. shadow and he has a cleft in his chin. He always hated shaving, but now he says it's easy and his 11 a.m shadow doesn't hit til mid afternoon.
If it weren't for the fact that the cartridges have gotten to be ridiculously expensive for what you get I'd have never tried to find ways to extend their life. But razor cartridges are like printer ink cartridges. The manufacturers could give you the blade handle and a printer just to lock you into their ridiculously prices supplies.