The tutorial told me that, when I select my settler, a blue circle will appear where it is most beneficial to found a city. However, I have seen the blue circle appear on squares that (as far as I can tell) have less resources on that tile than the tile right next to it.
What are the criteria by which a good location should be chosen?
I've heard it should be on fresh water, but I've also heard that the coast is better for trade.
Also, why does it sometimes take me 40 turns to make a worker at the beginning of the game, and in other games, with the same Civ, it only takes me 30?
Thanks
As mentioned above, ignore the blue circles and learn to trust your own judgment.
Founding a city on a tile right next to either a freshwater lake or a river will give that city a +2 health bonus. That's nice, but not essential--there are many other ways to gain health bonuses, and you usually won't encounter many problems with health early in the game.
What makes for a good city site? Above all else, food. Every city should have at least one food resource in its BFC (Big Fat Cross--the 5x5 area, minus the corners, that the citizens of the city can work after the first border pop). After food, try to include another resource tile (or more) and a mix of flat tiles and hills so you can have a balance of food (from farms), production (from mines) and commerce (from cottages).
In the long term, you will want to consider how to specialize the city. This involves choosing a particular focus for the city that helps you prioritize build decisions. You should ideally have a good mix of specialized cities in your civilization--commerce, production/military, specialists, etc. Check my Beginners' Guide (as recommended above, thanks, Valivator
) for an overview of specialization, then read up in the War Academy for more detailed treatments of the topic.
Coastal cities do get better trade routes, so more income. However, you will need to first research both Sailing and Writing and then have Open Borders with at least one other civ in order to gain the coastal trade route benefit. If you the map lends itself to having several coastal cities, building the Great Lighthouse can provide a powerful boost to your early economy.