Below the strain point, no significant annealing can take place. Annealing is much less a concern with forming glass only a single sheet thick because the temperatures at the skin and core of a single sheet can equalize fairly rapidly. Annealing single sheet pieces normally consists of nothing more than shutting the power off, and allowing the kiln to cool naturally, through the anneal point to the strain point. At that time, a small kiln post can be used to prop the lid open an inch or so for more rapid cooling. For thicker pieces, it may be necessary to turn the kiln back on as the temperature passes through the anneal point.
Thicker pieces have a much longer lag time for the core and skin temperatures to equalize.
Once the temperature has dropped below the strain point, the power can be turned off, but in this case, the lid should remain closed. Thicker pieces are also more susceptible to thermal shock. The most important ingredients of all in warm glass are imagination and inventiveness. Bake 'til done. Don't let it stick to stuff.