The right preparation is important: cleaning, crushing, etc. can be done much better before freezing than after thawing, e.g. also breading mushrooms. Take a look at the instructions for your appliance. Many manufacturers provide valuable information in this manual. Numerous websites also provide detailed advice.
Blanch vegetables beforehand or not? A question of faith that is objectively difficult to answer. A certain amount of nutrients is already lost before blanching. On the other hand, the remaining nutrients (because the enzymes are deactivated), as well as colour and taste, are retained longer.
Rapid freezing process
Ensure that the freezing process is as rapid as possible, because this is where the greatest loss of quality occurs (slow growth of the ice crystals destroys the cell walls and thus damages the texture, the fruit becomes "muddy"). Switch the appliance to full cooling capacity a few hours before (a largely filled one better the day before). Do not freeze too large packs and fill the bags as flat as possible. Do not place them on top of each other when freezing; you can stack them afterwards to save space. Do not freeze too much at once. By the way: you can also buy frozen food.
Setting the storage temperature
Set the storage temperature to at least -18 °C, better still below. Then almost all foods should be kept in appropriate packaging for approx. 10 months. A longer storage period makes no sense anyway, as a freezer is not intended for bunker storage in times of emergency.
Freeze thawed out again? From a microbiological point of view, no problem if something was just thawed or the defrosting phase was short. Bacteria hardly multiply at freezing temperatures, so there is no fear that this could damage your health. But the loss of quality can take on drastic proportions.
Do not underestimate the influence of the packaging: Unsuitable or too thin materials can allow oxygen or odours to penetrate. After removing as much air as possible, ensure that the seal is as tight as possible. (Leaks or too much air will cause freeze burning. This causes the surface to dry out. This is not dangerous, but the enjoyment value suffers.) Vacuuming and welding is ideal, as is a knot in the tightly twisted end of the bag. A wire paper clip is not ideal. Use cans only if they are leak-proof even when frozen and can be filled as full as possible. Do not burden your freezer by freezing odour-intensive goods such as onions or garlic, this can take revenge on the frozen cake.
Last but not least, you can keep an overview by labelling and keeping things tidy.