Simon...dont try to creat anything to outragous... the first thing I tried to do was a human head!!!it really messed me up for ages
Try the simple things like primitive shapes and editing the cv's on them th make a basic shape.
What I found was fun when I got going was to make a nurbs cylinder and to try to make a basic arm shape..kina bigger at the top and getting thinner on the way down.
helped with the cv editing also... plus its amazing what really basic shapes can do... make a big cube, cut 4 holes in and you have a house shape.
Try then to rotate a shape around for the roof....kinda simple but fun.
But dont set your goals to big to start...go easy, if you need more tutorials to help you join the VIP area
There are great examples of simple shapes for cool looking things...for example the "tie fighter" was just 1 sphere! just extruded out, then 2 cubes for the wings! as for what modeling to start with...well maybe start with polys as generally people find these a little easier to get to grips with
hope this helps