Initial settlement placement is crucial; aim for as many resources in the middle numbers- 5,6,8,9 - or place settlements around the same resources in those numbers to be able to effectively trade/maritime trade for the resources you need. But beware of the robber as if this sits on your hex you won't be able to earn ANYTHING!
PORTS: Placing one of your initial settlements on a port can be beneficial because it will allow you to trade in resources through Maritime trades right away, instead of having to wait several turns to build to one. BUT, you should only do this if the port falls between two hexes so that you'll be on two hexes and if the two numbers on those hexes are typically one of the stronger numbers (5,6,8,9). Keep in mind if this is your second starting settlement being placed on the port, you will receive only two starting resources. Also, make sure the port you choose will be supported by the placement of your second starting settlement (i.e. your first settlement is placed on a wood port and either the first or second settlement is on one or more wood hexes.)