I am no chef and am completely amazed at your ability to even consider doing this. Bravo on you!
I watch a lot of this TV show called Restaurant Impossible, in which chef Robert Irvine comes in to figure out what is going wrong with failing restaurants. He then helps them fix their problems. Sometimes the restaurant is out-dated and dirty, sometimes the owners have had no management experience, and other times the chefs were self taught (or placed into the family business with no training).
Here are some of the things that I’ve seen him help people with, especially with regards to inexperienced chefs. He will make each of the dishes from start to finish (usually after changing the recipe to something with better quality ingredients, or something that is easier to prepare, or something that looks better on a plate). Then he will take a picture of that dish. There will be photos, with exact descriptions of the ingredients, order of prep, and portions on this card. These “cheat sheets” are kept in the kitchen, right above where the prep is being done.
Make sure that you have proper measuring items, whether it be cups or a scale. To make sure that a dish is prepared the exact same way, each time, even if you make the same thing a hundred times, the best way to ensure that quality, is to make sure that you use the exact amount of ingredients, every time you make a dish. So that means, actually weighing the meat, or using the same amount of broth (with a measuring cup). You shouldn’t try to eyeball portions. The problem with that is because even if you are slightly off, the cooking time will be different, and you will have no portion control or inventory control. You need to be keenly aware of how much of everything that you are using for each dish.
And like the others have said, prep is essential, and the way that the prepped items are stored is very important too. Instead of having everything here and there, you need to have the items that you will be using for any particular dish, set out (and stored, not just left out, because cold items need to be kept cold) in the order in which they will be used. That might mean re-arranging your “stations” and your storage containers and your sauce bottles. And make sure that everything is labeled and that items that need to have lids, have lids and that you close the lids.
And yes, like @uberbatman said have your towels on hand. Make sure you use different towels for different jobs. Never use the same towel that you use to wipe your counters, or to dry your hands, and don’t use the counter wiping towels or your hand drying towels as your plate wiping towels (you know the towel that is used to clean off sauce spatter, when you are plating to make a nice presentation) You never want to cross contaminate anything with your towels. Have lots of clean towels on hand, because you will need to change them out often.
Figure out ahead of time (for your photo) exactly how you want your presentation to look, complete with sauce flourishes and sprinkling of garnishes. Take a photo of each item, and make sure that you use that image to create that same look, every single time.
Even accomplished chefs will constantly taste their sauces and other scoopable items, but make sure that you use a clean (and different) spoon, every single time you taste something. To do otherwise, is kind of like double dipping and very un-sanitary.
Instead of spooning your finishing sauces out of one of those square metal pans, and having to keep taking the lid off of it, or worse yet, having it kept un-lidded, store your finishing sauces in These Squirt Bottles and then keep the bottles in a refrigerated holding compartment, which could be another one of those square pans only bigger, but that is either refrigerated from below, or filled with ice. And make sure the bottles are labeled (on both sides, because they’ll get turned around) and kept in order, so that you can just grab one and not accidentally grab the wrong sauce. Put them back in the correct order, each time.
On your own, learn all that you can about the laws and regulations of food safety. That is a big issue on Restaurant Impossible, with regards to the way food is handled (actually prepared and cooked) to the way it is stored, with regards to temperature, cleanliness, and even whether certain items are stored above other items, or whether a shelf needs to have a flat bottom or have open rungs (for air circulation) and how often to rotate out older items. There is tons of information (which I don’t have, but have seen Robert Irvine discuss it) about the proper storage and handling of food so that one doesn’t cross contaminate or create a food safety hazard.
Here is just a small List of things that need to be cleaned on a regular basis, in a restaurant kitchen.
You are going to have to start doing a lot of homework to learn all you can about the restaurant biz. I realize that you are in Spain, but This Site can give you some ideas of what you will need to know about food safety. I imagine they have similar sites with regards to rules and regulations in Spain.
Also, here is some information about how to prevent Cross Contamination
Here is some information about how to Organize a Commercial Kitchen
This is geared towards restaurants employing young people, but since you don’t have much experience, This Info will be valuable to you too.
With regards to how to make all of your dishes come out cooked properly and at the right time, on time and all of that jazz, I can’t help you there. I could never do what you are doing. It still amazes me how my Mom is able to put together a Thanksgiving dinner, without looking at a single cookbook or guide. She learned from my Grandmother and she just knows how to do it. Unfortunately in your case, you are going to have to learn from the internet (which is not nearly as much fun as learning from your Grandma, and not as useful as learning from a culinary school).
I wish you the best of luck, in both your new job, and with your new relationship! I really do admire you!