Tips
In Cities & Knights, you roll 3 dice at the beginning of your turn: 2 production dice and 1 event die. 3 sides of the event die show the barbarian ship. This means, there is a 50% chance per turn for the barbarian ship to come one step closer to Catan. Considering this circumstance, it may take only 3 or 4 turns until the barbarian ship lands on Catan.
Therefore, it is important to start building knights early in the game and to activate them. Such preparation will help you avoid being the target of the barbarian army, i.e., losing a city. Grain is very important for defending Catan. Knights are of no use as long as you don't have grain to activate them.
There are certain “house rules” that may soften the impact of the barbarian attack at the beginning of the game. You can, for instance, declare the first barbarian attack void or allow each player to have one activated knight at the beginning of the game.
Personally, I am not a big fan of such variants. One major appeal of the game is attributable precisely to the threat of the barbarian army,which you have to prepare for as early in the game as possible and include in your strategic planning.