What Are The Most Important Things To Remember When Cooking?

Hygiene is key to cooking. No matter how good it tastes, if its not safe you can become ill or even die. Cross contamination, do have cooked food and raw food near each other or use the same knives forks and spoons on both. Cutting boards must be sanitary. Remember when storing food in your fridge, cooked food on upper shelves, raw on bottom. Wash hands in between handling raw chicken and other meats. Food borne illness can be fatal especially to children and the elderly.

The two best pieces of advice I ever heard were from chef Ken Holm: always buy the best ingredients you can afford; and don't experiment on your guests. Try out recipes in advance.
Other handy general hints include:
-Get everything ready and weighed out before you start – you'll need the time later.
-Write down timings etc –keep them for future reference if you're doing this dish again.
-Allow enough time to enjoy the process (and have a margin for error.)
-Any spare money should go on sensible cooking equipment like very sharp knives and sturdy cooking pots, rather than fancy gadgets which you'll only use once. (on the other hand, useful multi-purpose gadgets like food mixers are a great investment.)
To begin with, use a trusted cookery book and follow the recipes meticulously – you'll soon develop your own style, but at first everyone needs guidance.
Don't be put off by failures – have another go.