If food has been frozen, ensure it is completely thawed before it is cooked. Otherwise it will not receive the actual time and temperature ratio you thought it did, some of that time will have been spent thawing out, not cooking. However, some foods may come with cook straight from frozen instructions - this is fine as extra time has been included. Follow the instructions and probe the food, when finished, to confirm it has reached the right temperature for kill off of bacteria, which is 80°c.
In preparing foods, raw foods must be kept separate from cooked or ready to eat foods to prevent cross-contamination between the different food risk types. You must either:
Thawing must be done either quickly in a microwave or slowly in a fridge or chiller. Again, the time at room temperature must be minimised to prevent bacterial growth. If a microwave is not appropriate for that food type, you are simply going to have to get more organised to allow the time it will take to thaw the food in the fridge or chiller. Some foods can be thawed under running cold water, but it depends on whether this waterlogs the flesh or not.
Do not refreeze thawed foods. If they been thawed accidentally they must be eaten straight away or cooked and then refrozen if need be.
Cooking times and temperatures must be sufficient to ensure that all bacteria and their toxins are destroyed. If they are not, re-increase of multiplication may occur during cooling or incorrect storage of cooked food.
Food must be thoroughly cooked right through. Preheat the oven so that the food had the correct temperature right through the cooking time and probe the food once you think it is ready to ensure it has reached the correct temperature. Juices should run clear, any joints should move freely and it should be piping hot. This is especially important if the food has been cooked in a microwave as you cannot determine what temperature it operated at.
To probe for food temperature ensure you sanitise the probe first and insert it into the deepest part of the food. It is best to check a number of different sites. In poultry, check the thigh joint, not the abdomen as this may be hollow, and you're looking for the meat temperature not that of the stuffing.
You also need to check your thermometers against each other to ensure they are accurate. It is best to get a reliable thermometer that can be calibrated. Your whole business hangs on your thermometers' accuracy.
When using a microwave, ensure you turn or stir the food for even cooking, allow the standing time at the end to finish the process, and check it before it is served to ensure the cooking has been even and thorough. If using a microwave it is best to follow microwave specific recipes, as microwaves are easily misused with resulting unsafe food.