I'm not totally sure what you mean but anyway... hope this isnt just waffle!
When your wheel is set dead in the middle then the car will go in a straight line, but as you say roads arent perfectly straight. Go to some quiet roads where you can have a play around with out too many cars nearby. Try putting the car in the road - where it should be in normal driving and let the wheel go to the middle so the car is going straight. Try turning the wheel a very small amount to the left as the car is moving slowly - see how much the car moves for not much turn on the wheel. Take it back to the middle and do the same for the right. Just for following the natural bends and curves in the road you wont need to turn the wheel much at all - try and get a feel for how much turning the steering wheel turns the car.
Then as jr2007 said, try and get used to what you should be able to see out of the windscreen when you are in the correct driving position. The 'correct' driving position will change abit depending on the width of the road - if you are on a wide road there is no point sticking into the kerb, but if it is a narrow road then you will obviously have to be closer to it.
Also, make sure that when you are driving you look at where you want to go, it sounds silly I know, but if you look at the kerb, you will tend to steer towards it. If you are looking ahead down the road you are more likely to follow the road better. Make sure that you look quite far down the road as well, my driving instructor kept going on about near, middle, far. Look at each in turn - dont just look close to you, if you are focussing too much on the 'near' then you are just following that part of the road - try and look ahead so that you can see a bend etc coming up and can start to move the car into the bend better.
Hope that is some help - and that I havnt totally misunderstood what you were asking!