Here are my tips for new cooks:
Forget the fancy kitchen gadgets until you have stocked the boring basics: a good 4 quart pot (preferably a tri-ply pot; I like Cuisinart Multiclad Pro), an 8" or 10" nonstick anodized skillet or ceramic coated skillet (I use Cusinart Green Gourmet), a good 6" or 8" cook's knife and sharpening steel (I use Wüsthof Classic), and a bamboo cutting board. With a little creativity, you can manage a LOT with just these items.
Prewashed greens that can be either cooked or eaten raw are an awesome, healthy timesaver. For example: arugula, spinach, arugula/spinach mix, or my favorite: OrganicGirl Super Greens. When I'm cooking well, my partner and I will go through 1 to 1½ pounds of greens a week. That's a LOT. They will seem expensive compared to a head of lettuce, but you can throw them in anything: salad, pasta, quesadillas, sandwiches, quiche… with no prep. Ultimately you will save money, rather than eating out or buying a salad for lunch.
Onions and garlic are cheap and make almost everything (well, everything savory) taste better. You will discover that if any guest walks into your house while you are sautéing onions and garlic, they will assume the food tastes awesome because it SMELLS awesome. They are really good for you, too!
Scared of that onion? [Megan's note: yes!] I promise you, when you are faced with something you don't know how to do, there will be a video for it. Particularly, learn how to dice an onion here.
Eggs are excellent, healthy, cheap protein and can be made in a million ways. Ditto for beans.
Start with easy vegetarian recipes That way you can take your time learning about all the food safety issues you have to be aware of when cooking with meat, especially poultry and fish.
Choose and acquire 2-3 quality spice mixes that you can experiment with until you know spices better. Quality is sometimes more expensive, but you will not waste it because it tastes good. I especially like: Penzey's Mural of Flavor (awesome in eggs, tuna salad, salad dressings), and Penzey's Maharajah curry powder.
Pasta is easy, inexpensive, and fast. Try whole grain or quinoa pastas to increase the nutritional content. Always read the instructions, since cooking time varies pretty radically, and never forget to salt your water. Don't forget couscous — a super easy, super fast pasta.
Eat the rainbow. Not every day, but during the course of the week, try to get foods with a variety of colors. Those colors often indicate specific nutrients!
Frozen veggies are not the same thing as frozen pizza. They are inexpensive, flash frozen almost immediately after picking, and keep their nutrients better than fresh foods that have been sitting in your fridge for a few days. So have a few bags in your freezer and don't be afraid to use them!
Always read the whole recipe carefully before you shop, and again before you start cooking.
So, what's YOUR one best tip for new cooks?