The first step of raising a successful metropolis is finding a suitable place for it. You have to know what type of city you want to build from the very beginning. Different types of cities have different terrain preferences.
First of all let's look at general factors which we should consider when looking for the best place to start a city:
Good terrain for development - most obvious and most often used factor. The good idea is to avoid placing cities near other cities' terrain whenever possible - every part of territory already used by another city is useless for the new one.
Secure important resources - especially strategic ones. It's most important when it's likely that one of your competitors can overtake you in the race for this particular resource.
Military reasons - good placement is the best defence for the city. Bonuses form culture, buildings, terrain (hill and river) and eventually well planned units' promotions can make your city insurmountable castle.
Limiting your opponents' expansion - without Open Border Treaty no civilization can enter another one's territory without triggering a war. Well positioned city can cut off some big parts of a continent from your competitors' settlers - and save it for your own people.