Center of the "tops" when climbing, getting upright to use the glutes to power up a slow paced climb. Outside (round part) of the tops when standing on a climb. In the drops when in a tough or sustained upwind or on a fast long downhill/downwind. On the hoods when in a mild climb where the wind isn't a factor, or in a group where I'm not off the front. Also I get on the hoods when I need control, such as on steep descents or heading into corners. Mix it up whenever the mood strikes me.