Part of food prep is having fresh ingredients. Old slimy veggies are unappetizing and hard to cook, same with dry or slimy meats. Freezing most meat is fine, refreezing on the other hand is not so good.
That being said: food prep starts at the shopping list and into the actual shopping.
Always make sure your ingredients are how they are supposed to be. As above, keep things fresh. It is very important when using non-standard flour that you either sift it or something similar with a fork to make it uniform and light. This goes for things like baking powder and erythritol and spices too. I’ve noticed that almond flour clumps quite a bit, so I usually use a fork to smooth it out
What you see on TV and in food making videos where they have spices perfectly portioned out is slightly unrealistic, but doable. It is way better for the ingredients to do so however. If you use dry spices including salt and pepper while cooking stovetop, it will add some moisture to the rest of the container, clumping and/or spoiling it.
For some meals, you can prep the entire thing, others are harder to do ahead of time. I like to cut all my veggies at once just before I use them. If I am making something that uses lots of veggies, I put them in a large bowl to set aside, otherwise I can add them in the order they are cut.
Food prep also includes whether you want your avocado whole or mashed, for texture, presentation, or the fact that squishing it keeps it from sliding out of sandwiches so easily. Keeping things you want to do with your food in mind, helps shape the rest of your prep.
Meat, for the most part, should be left out to get to room temperature for 30 minutes before cooking, and left to rest for 5 minutes afterward.
Since you do not want to re-cook things if you can avoid it, unless you don’t have the time or access to the kitchen, you’ll want to make everything fresh.