1) Lumpy sauce or gravy? Remember hot and cold - either hot roux and cold liquid or cold roux and hot liquid. If you still end up with lumps just puree sauce with an immersion blender.
2) When juicing citrus fruit, roll on the counter for 15 seconds to get the most juice out of them. Remember to zest the fruit first before juicing.
3) Allow steak to come to room temperature before cooking for the best results.
4) Fresh parsley and cilantro will last a lot longer if you treat them like a bouquet of flowers - stems in a glass of water, cover loosely with a plastic bag and keep in the fridge. Change the water every couple of days.
5) Taste everything. That is the only way to know if everything is seasoned perfectly. If you are making something that is unsafe to taste raw such as meatballs, make a miniature patty and cook in a skillet or microwave for 20 seconds. Taste and adjust seasoning.
6) Invest in a good set of knives, it will be the best investment you will ever make. There is absolutely nothing worse than a cheap, flimsy, dull knife. Dull knives are actually far more dangerous than sharp knives.
7) Blot meat dry with a paper towel or clean kitchen towel before browning. If the meat has any moisture it will just end up steaming instead of browning. The same rule applies to sauteing fresh mushrooms.
8) The easiest way to remove fat from a soup, stew or stock is to refrigerate overnight. All the fat will rise to the top, just scoop it of with a slotted spoon. If I don't have the time for that, I add a bit of chopped parsley to the soup. The fat and the parsley will float to the surface so it is easy to see it.
9) When cutting up round fruit and vegetables, such as potatoes, cut a piece off to make a flat surface so that it doesn't roll around. It will be much safer and easier to work with.
10) Don't sweat the small stuff. Cooking should be fun. Almost every cooking mishap can be rectified. If not, there is always take - out.