1. Don't raise the lid
You might be tempted to lift the lid for a quick peek or to see how your food is cooking, but it's imperative that you fight the urge to do so. A crock pot is designed to cook food over a long period of time and if you lift the lid off, even if it's just for a few seconds, the heat that has built up will be lost. The only exception to this rule is when you are adding food right at the very end that only need a short time to cook (dairy products and herbs).
2. Don't use the wrong meat
Cheap and less tender cuts of meat such as chuck or flank are ideal to use in a crock pot. Save the more expensive and tender cuts of meat such as steak or sirloin for the grill or stove top. The aim of a crock pot is to turn cheaper cuts of meat tender, so why waste money by throwing in expensive and already tender pieces of meat? It just doesn't make any sense.
3. Don't use raw meat
Browning your meat in a skillet caramelizes the flavor and seals in all those lovely juices. Adding raw meat to your slow cooker will work, but it just won't have the same flavor. Sear it first - it is a good idea to coat it in flour before you sear it since this helps to thicken the sauce without having to add extra flour or cornstarch later.
4. Don't use too much alcohol
On the stove, wine and other alcohol spirits reduce in volume and help capture the flavor. However, in a crock pot, this does not happen, so the result is a dish that tastes too much like raw alcohol. Use a broth, or reduce some wine on the stove first before adding to the crock pot.
5. Don't use chicken with skin
Unless of course you like the taste of rubbery and tough chicken skin, it'll not be crispy enough in a slow cooker any more than it would on the stove over a low heat. Bones are different though and these should be used with abandon, as they make the chicken more tender and flavorful.
6. Don't add fresh herbs too soon
If you add the herbs to soon all their delicious flavors will be lost. Add them during the last half hour and you will experience a burst of flavor throughout your dish.
7. Don't forget to layer properly
The bottom of the slow cooker should be used for those foods that take the longest to cook, such as root vegetables. Doing this ensures that the different food layers cook evenly with everything being cooked at the same time.
8. Don't add dairy products too soon
If you add dairy products too soon, they may curdle and ruin your dish. Just like with the fresh herbs, dairy products should be added during the last 30 minutes of cooking.
9. Don't overcook
Just because a slow cooker allows you to cook something for 10 hours, doesn't mean you should cook something for that long. If you can, invest in a slow cooker which has a timer as overcooked food will be severely lacking in flavor.
10. Don't forget to vary your cooking time
If a recipe says 4 hours on high or 8 hours on low and you're thinking of making it more than once, try it both ways and see which one works the best for you.
11. Don't forget to cover the meat
A slow cooker works best when everything is submerged, as this ensures that the food cooks evenly. Don't just place that cut of meat on the top as it will dry out. Place it in the center of the pot, on top of tougher vegetables and surrounded by those that will cook more quickly, and then add the liquid.
12. Don't fill the slow cooker too full
Most slow cookers suggest that you only fill it 2/3 full. The reason for this is that if you fill it to the top, the ingredients will steam instead of simmer.
13. Don't believe that you can cook anything in a crock pot
Sure, it's possible to find recipes for crock pot pasta this and that, but surely you want al dente pasta and not mushy pasta? Let's face it, some things are better off being made on the stove.
14. Don't use a crock pot to reheat food
Why would you really want to do this? The microwave is there to reheat food in minutes while the crock pot is designed for slow cooking.
15. Don't under fill the slow cooker
If your crock pot is less than 1/2 full there is a very good chance that your meal will be burnt by the end of the cooking time.