Increase the temperature by directing the solar cooker regularly at the sun. Increase the surface area of the reflectors. Add insulation. Angle the reflectors so the light bounces towards the food.
Decrease the temperature by not directing the solar cooker directly at the sun or make a small opening in the glaze to allow some heat to escape.
Clean the glaze to allow more light to shine through.
If using jars with lids to cook food. Do not tighten them all of the way. Steam needs to be able to be released.
The same amount of food will cook faster in multiple smaller pots than one big pot.
Shallow cooking containers cook faster than deep cooking containers.
The best time to cook is around 10am - 2pm.
Preheat your cooker (UNLESS it is a vacuum tube cooker. The thermal difference when you add the food may break the glass.) It helps you judge the time better and is safer food handling for more perishable foods like fish.