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Waiting for Investment Cards

Since each investment card multiplies the points gained from a site, its a good idea to try and wait for investment cards. Early in the game it may be better to discard and wait for investment cards then to begin exploring a city.

Focus on a few colors

Splitting your focus between too many colors can be detrimental. The initial exploration cost is fairly hard to recover. Trying to focus on two or three colors can lead to far bigger gains especially with a few stacked investments.

Stalling

The game ends when the last card is drawn from the deck. You can draw the game out awhile longer by taking advantage of the ability to draw discarded cards. Near the end of the game, this can help squeeze in a few extra moves even if it means drawing a useless card from one of the discard piles.