Not wage wars of aggression.
A military is a necessary evil. There are among us many who would rule the world for their benefit at the expense of their victims.
Abandon delusional beliefs regarding life after death (tell that to suicide bombers). Make people aware that life is precious.
http://images.search.yahoo.com/search/images?_adv_prop=image&va=Bali+bomber+to+be+executed
Commit oneself to rational living, clear investigation of reality. This requires education about the real physical world, how fragile its resources are. People fight over these resources but often lack foresight and knowledge of how to manage them well.
Spread the culture of science to combat superstition and ignorance. People are intolerant of competing delusional belief systems; that is the history of religion. It would help if people actually knew that we evolved as a species and that we are not the special project of some god. Teach young people how to avoid falling prey to culturally acquired delusions, and how to think critically.
Teach people about physical anthropology so they can abandon failed race theories.
http://humanorigins.si.edu/evidence/genetics
Oppose ethnocentric nationalism everywhere it is found. That is what NATO did to Ratko Mladic and his fellow psychopathic killers.
http://www.historyplace.com/worldhistory/genocide/bosnia.htm
http://www.un.org/preventgenocide/rwanda/infokit.shtml
Limit the spread of nuclear technology. It has overall been more trouble than it is worth. Now that it is widely known how to make nuclear weapons, people will make them. Some of those people are paranoid and authoritarian. So if possible it must be suppressed.
Support universal health care. You have it in Canada, we in the United States do not. In developing countries there is very little health care.
Support equitable distribution of resources whenever possible. That is very unlikely to happen any time soon.
Grow corn for food not fuel, at least in North American, since the latter drives the price of food up in developing nations; people will fight for food, and rightly so. While a small minority profits, other people go hungry.
http://en.wikipedia.org/wiki/Food_vs._fuel
Stop growing beef on land that could be used for food production. Stop eating the stuff, change to a diet for small planet whenever possible.
http://www.globalissues.org/article/240/beef
There is always going to be aggression among human beings. Educating people from early ages to understand the nature of the world they live in, and how we know about it, would go a long way in helping them resolve complex issues regarding resources. World resources cannot be managed well without cooperation.
Knowing the real history of our species and of civilizations would also help. Learn from the mistakes of the past.
Between Pakistan and India there is a very long history of the conflict between two cultures that goes back hundreds of years before the partition of India in the 20th century. They stock nuclear weapons to use against one another over that conflict. It can never be resolved as long as they cling to their delusional beliefs. Pakistan is a paranoid state, overall. What to do about this? For one thing, keep the weapons out of the hands of the Taliban and similar groups. That involves military activity, there is no way around it by negotiating; the Taliban is authoritarian and without moral or ethical concerns.
http://www.ndu.edu/library/docs/crs/crs_rs21237_17feb05.pdf
So unfortunately there cannot be peace just by not waging war.
Some people need to be suppressed so others may live. Osama bin Laden was both a psychotic and a sociopath. Other people's lives meant nothing to him and there are many more like him. It is not possible to live in peace with these people, for they will attack no matter how well others are getting along. They behave according to bizarre, antisocial and paranoid delusions. They will never be disabused of their irrational beliefs or antisocial attitudes.