Normally it is only after you have demonstrated the ability to turn reasonably well (coordinating the stick and rudder) that the instructor focuses on you flying accurately in a straight line.
 Turning over Hawaii |
I was told that flying accurately in a straight line can be harder than turning and is often mastered a little later in training. It is actually a sequence of rapid and small "anti-turn" adjustments to counteract the tendency of the glider's heading to drift. I noticed too that the compass tends to lag and swing more than expected when manoeuvering, so that a really steady path is required for it to settle down. |
Once as I flew us "straight" hoping to find another thermal, the instructor pointed out that I was holding the left wing a little low so we were turning very slowly to the left. He reminded me that it helps when flying straight to always have a target in mind - i.e. fly the glider towards a distant landmark like a mountain peak. You should always purposefully fly the glider rather than let it drift. Many people have a tendency to apply a little stick or rudder by accident which cause a slow turn or extra drag respectively. And if you let the glider drift it will tend to avoid thermals as the rising air on one side will lift that wing and turn you gently away from the thermal.
One key point is that until you can fly accurately in a straight line, you are not really ready to try an approach and landing.