The most effective way for a ruler to maintain power

I think the most effective way for a ruler to maintain power is by diplomacy. First of all I think a ruler should not be allowed to rule his whole life. But for a ruler to rule correctly and keep the country peaceful, at least internally, he must be diplomatic but able to use violence if necessary.
A ruler must rule peacefully. If a ruler builds hate between the people of his country then there is a chance that civil war will break out. So in order to keep peace a ruler must be unbiased and treat all his people with equal respect. He must also try and avoid actually killing or hurting people in his country. Because lots of death means sadness, and sadness means hate and hate means more death. And it's a circle that if started will never end.
If a ruler rules his whole life he will get corrupt. It's just in the human nature, if you have too much power you don't want to lose that power. Then you get paranoid of losing your power and take steps that will keep you from losing your power, these steps often involve hurting people. So I think a ruler shouldn't be allowed to rule his whole life but should be allowed to rule like the president is in America.
Lastly I think in a order for a ruler to keep his power some violence is necessary. I mean if there's a rebellion well you obviously have to send in armed forces. But I think it shouldn't get to the point of Nazi Germany, where everyone who talked bad about the Nazi party was either killed or put in jail.
I conclude that the best way for a ruler to maintain his power is by being nice to his people, participating in there events (making speeches, being active in general), only resorting to violence if necessary, and not spending too much time on his own enjoyment like not being too flashy. Aside from obvious stuff like running the government good, not going to war for reasons that seem invalid to the people, and keeping the country away from invaders.