Build two rings of cities (about 20 cities, std map size) capital being at the center of the first ring then build the FP at the city center of the segond ring.
Then build library, university, research Lab but also Market place, Bank, factory and plant in all core cities. Temple and Cathedrals for keeping Pop happy.
If you do not finish your game early, you might have to sell a few Temples to avoid a cultural victory.
As Moonsinger wrote give tech to the other Civs. Especially Scientific's Civ who gets a free tech at the begining of new age, go for Engineering and deal Monotheism with Scientific Civ, that way you will have a Tech without searching for.
You also can trade Tech for ressources.
Regarding Diplo Victory, just build the United Nations and click NO when time for voting comes, you won't take 'a chance' to win by Diplo.
Keep your military low in number, do not upgrade but build new and disband old units in cities where shields are needed.
Hope it help, GOOD LUCK !