Disclaimer

Much of the following only applies to 2-player games as this is the competitive format. With more than 2 players things get a little crazier because only the level 1 resource numbers change, so all the decks cycle much more quickly. Generally speaking this means that resource production buildings are better and point production buildings are worse as there are more players who can grab and hold those resources. Kingmaker situations are common.

Early Game

• Securing buildings that give level 2 resource production is crucial, but not at the cost of your entire economy
• First player must trade for 3 level 1 resources based on what's currently shown - trading for a single level 2 makes it too easy for the opponent to block
• Second player has the option to trade for and effectively block one of first player's level 2 build options - this can be a good idea if that resource builds into a powerful building like coal, stone, or brick production
• Consider trading for all of one or more level 1 resource types to prevent the opponent from being able to buy certain cards - this is particularly effective for wheat or stone, but is applicable for clay or wood in some cases

Midgame / General Strategy

• Pay attention to what resources your opponent is grabbing - buying cards out from under your opponent can be pivotal
• The game is played in cycles of building up high value cards and then trading them down for buildings or more resources - it's important to not spend all of your resources on buildings i.e. try to keep at least one 3+ value card to trade your way back into production
• If a player is low on resources, it is easier to hamstring them into no options but slow production - always keep this in mind for yourself and your opponent
• Watch the discard piles and deck sizes. If you can, spend the resources you produce via buildings before the deck is reshuffled as rebuilding those resources is free value. Conversely, try to buy and hold resources your opponent builds freely so they do not get the extra value
• When producing a resource always consider what the next card of the deck could be. In some cases waiting to use your building to produce at the start of your turn is better to give your opponent one less option. In other cases, producing it now is better because the opponent would otherwise buy it out from under you.

Late Game

• Building up high resource value is great, but never forget that the only way to win is to reach 10 points. Plan out turns in advance to see if it's time to flip the switch and just buy buildings or if continuing to increase resource value makes sense
• Pay especially close attention to cards that convert resources to points as a player can win in one turn from as low as 6, 5, or even 4 points in very rare cases - with proper planning it should be easy to block these sorts of plays