Getting a seat on the subway can be nearly impossible in Asia. The locals are just too quick to snatch them up. Unless you wanna be a jerk and push them out of your way you will likely be standing all the time. This sucks, especially if you have flat feet like me.
Your best chance of snagging a subway seat is to walk all the way to the very first or the very last car. Those cars usually have the least amount of people because people are just too lazy to go that far. I have been able to snag seats in Japan, China, and Singapore by doing this. It doesn't work 100% of the time, but it beats standing 100% of the time.