Swallowing your pride and paying up tribute demands helps a lot.
If you don't want a war, try and stay in the same religion as the more psychotic leaders. Once you have decent relations, they readily accept bribes to attack other civs which will keep them busy and permanently taint their relations with the victim civ.
Check the diplomacy screen of aggressive leaders, under the declare war section if they have "enough on their hands" it means they are planning an invasion of someone (either you or another AI)
Finally, if you have a neighbour that you can't get along with and expect to be fighting eventually, either attacking them first when you have a military tech edge or bribing someone else to attack them is the best form of defence.
If you don't want a war, try and stay in the same religion as the more psychotic leaders. Once you have decent relations, they readily accept bribes to attack other civs which will keep them busy and permanently taint their relations with the victim civ.
Check the diplomacy screen of aggressive leaders, under the declare war section if they have "enough on their hands" it means they are planning an invasion of someone (either you or another AI)
Finally, if you have a neighbour that you can't get along with and expect to be fighting eventually, either attacking them first when you have a military tech edge or bribing someone else to attack them is the best form of defence.