I'm not a nutritional expert nor have any training in the field.
I can only tell you what I've learned and my own quirky ideas on nutrition.
Eat plant based for the majority of your calories. Fruits, vegetables, nuts, whole grains, etc. Then the rest is dairy, fats, sugar, meat, etc.
They say the "average" serving of meat is about the size of a deck of cards. That obviously would never ever work for a steak so I ignore that when the T-bone or ribeye hits the plate.
I've read in several different places over time that it takes precise planning, weighing and work to make sure you are receiving 100% of all your nutritional needs from food every day. Take a multi-vitamin, it's much easier. If you're not a big dairy drinker/eater, take some calcium with vitamin D too.
I'm not one to ingest chemicals. I don't like anything fat free or that has been modified from it's original form. If I have toast, I use real butter. I don't slather on 4 tablespoons but will use about 1 tablespoon. Butter's ingredients are cream and salt.
Promise Fat Free Heart Healthy and all that jazz has a laundry list of artificial ingredients, preservatives, artificial coloring, monoglycerides and diglycerides which I don't even know what those are . . .
Real sour cream contains milk, cream and enzymes. Fat free sour cream has Cultured Lowfat Milk, Modified Corn Starch,Whey Protein Concentrate, Propylene Glycol Monoester, Artificial Color, Gelatin, Sodium Phosphate, Agar Gum, Xanthan Gum, Sodium Citrate, Locust Bean Gum, Vitamin A Palmitate, yuck.
But personally, given the choice, I'll eat something natural, in it's natural form over something manufactured because I think it's better for me then ingesting all those chemicals.
You can make changes to food you already eat by switching the form you eat it in. Change regular english muffins to the whole grain type. Change regular eggs to ones the chickens have been feed grains, no antibiotics, that are high in Vitamin E and Omega 3. Try not to eat the fat off meat, and choose lean cuts. Change white bread to whole grain bread.
Frozen vegetables are supposed to be higher in nutritional content because they are processed and frozen quickly after picking, fresh produce is covered in waxes and sprays and may not be as field fresh as you think. Farmer's markets are great for fresh produce.
Snack on nuts, fruit, raw veggies, protein bars, popcorn, baked chips (baked!) and don't discount dried fruit, some of it is pretty tasty.
Something you can try is get a vegetarian cookbook. All the recipes will be plant based, beans, rice and generally healthier for you. Then you can add chicken breast, or shrimp, fish etc. to recipes that you like.
Here's a list of vitamins and minerals, what they do and the foods they can be found in:
Vitamins and Minerals - what they do and the best food sources
Good luck in your new endeavor!