My Key Strategy is to build as quickly as possible on as high numbers as possible and to have as many of the 5 resources as possible. To have a good brick and wood resource to start with is very useful, wheat is generally the next best.

Make sure you are able to get to a reasonable iron ore and wheat or you will not be able to build city's, which are crucial to winning the game.

It is well worth getting to a port if not to start with by mid game and if a resource has only one good number i.e 6, 8, 9 or 5 try and get it if possible.

Longest road and biggest army are important, but not as important as fast building on good resources to start with. It is good to trade with those who are not doing so well where possible, but better to trade with anyone other than someone who is winning rather than trading in for a 4:1 or 3:1 port.

Hope this Helps

Martin.