Do you leave the lights on when you are no longer in the room? Modern lamps consume little electricity, but it is still worth not leaving them on unnecessarily, for example when we are not in the room for a long time.

Let's be honest – do you walk around your flat in a T-shirt in winter too? Most living rooms and bedrooms are too warm in winter – we walk around in T-shirts instead of putting on thick slippers and jumpers. The potential energy savings here are considerable.

Intelligent ventilation means not too late and not too long. It is too late when we become tired from stale air, get headaches and the humidity becomes too high. It is too long when the air has already been exchanged and is cool, but we continue to ventilate and then the materials (walls, furniture) also cool down. Ultimately, heat means that things or air vibrate. When the air has been replaced but the objects and walls are still vibrating, the fresh air quickly warms up. If the walls also become cold, mould can form on them and we need expensive heating energy to get everything vibrating again. CO2 measuring devices help to ventilate at the right time and not for too long. However, these should not be useless gadgets, but perhaps used to practise one after the other in the rooms and also lent out. A nice game is to compete to see how good people's sense of timing is when it comes to ventilating at the right time and not for too long.

Do you have a large (0), medium (1), small (2) or no (3) room of your own? The space we need to live in means the area that is sealed, the building materials that are required and the space that needs to be heated – and all this must also be considered in the context of social justice. When more people live in a household, they share rooms such as the kitchen, living room or bathroom. In fact, the per capita area is increasing continuously because more older people are living alone and longer in large houses and because there are more single households. Not everyone can renovate or move out, but those who take these steps can be proud of reducing their living space. Very few children and young people can decide how big their rooms are. But those who have a small room or share it with siblings can be proud of it and collect the points.

Long, hot showers mean water and energy consumption and ultimately high costs. The further effects are even more impressive when considered in context – did you know that long showers can be responsible for refugees and the quality of life in Germany?http://www.imodeler.info/ro?key=Ceju1XNHCFZBJc2MpbAOl5Q

Unlike a vegan diet, a vegetarian diet can also include milk, cheese or eggs, but no meat or fish. Vegetarian days are healthy, mean less animal husbandry and thus less consumption of land and water. We Germans consume more than three times the amount of animal products that the EAT-Lancet Commission says would be healthy for us and the planet. The World Health Organisation (WHO) even warns that meat consumption can be carcinogenic – but so can cheap tofu sausage.

Being vegan means abstaining from fish, meat, milk, cheese and other animal products. For many people, this is unthinkable, partly because of the taste and partly because they consider it unhealthy. As far as taste is concerned, there are so many different vegan alternatives that you are bound to find something that tastes just as good or even better. We just have to try it – from vegan cheese to egg salad to burgers. Many celebrities and athletes are vegan. Veganism is booming. As for health, our early ancestors ate a healthier diet than we do today. They ate a mixed diet with little meat and fish and also little grain, but more legumes instead. Those who follow a vegan diet need to pay attention to two nutrients: vitamin B12 and unsaturated omega-3 fatty acids. B12 is available to buy in lozenge form (or as an additive in foods that are then no longer labelled as organic). Omega-3 fatty acids are found in linseed oil and algae oil. After a few months of following a vegan diet, a blood test can show whether there are any deficiency symptoms. As a rule, vegans eat healthier and are fitter than others. What else does it do? In addition to ethical reasons (keeping and killing animals), vegans help prevent deforestation, as most of the world's land is used for animal feed. In fact, we will not be able to feed the growing world population in the same way that we Germans do. Vegans also prevent greenhouse gases from being emitted by cows in the form of methane, save enormous amounts of drinking water and prevent soil, groundwater and waterways from being polluted. Incidentally, this is the greatest leverage young people have for a better world – provided they are allowed to have a say in what they eat at home.

Do you sometimes throw food away? Or do your parents throw away food that you didn't eat in time? Food is wasted from the field to the factory and transport routes to the point where we, restaurants and supermarkets throw it away. Ultimately, this means that more land is needed for cultivation, which leads to deforestation and endangers biodiversity with pesticides and fertilisers. We can shop more selectively, avoid throwing away products just because of their best-before date, save food in the household (e.g. freezing bananas or making long-life spreads and soups from leftover vegetables), saving specifically rescued food (e.g. goods that are too small or shriveled) and, in many places, donating leftover food, e.g. to food banks.

Consistently separating waste, including green waste, glass and paper, is not as self-evident as can be assumed. Many make little effort here and don't really know what belongs in which bin. But also special waste, such as batteries, incandescent lamps, electrical appliances, etc. must be disposed of properly.

Tap water is preferable, possibly with homemade juices. Otherwise, use returnable glass bottles with drinks from the region. Plastic bottles are problematic, drinks cans are very bad, and Tetra Paks are not easy to recycle.

A lot of things are actually thrown away, even though others could still use them. It is more convenient for us not to repair them than to have a stall at the flea market or to have to send them off for little money. But the good feeling of doing the right thing is motivating.

Do you ever wear very old or second-hand clothes – perhaps from your older siblings? Many people enjoy the variety that new clothes bring, or simply grow out of their clothes quickly. Those who only wear clothes for a short time should try second-hand clothing and at least sell the clothes they no longer wear or donate them to a charity shop. Others wear few items of clothing without any desire for variety until they fall apart. Of course, this works best with higher-quality clothing.

Many devices from vacuum cleaners to cordless screwdrivers to TVs are amazingly inexpensive today. Relying on valuable devices that last a long time, or even buying used devices, helps to save raw materials and energy. Look for refurbished products.

Precisely because equipment is so inexpensive, we tend to buy all kinds of equipment ourselves rather than borrowing it, whether from neighbours or tool rental companies. All the major DIY stores now offer a rental service. Children and young people can also borrow and lend items – whether toys, clothes or anything else they need for their next party.

Unfortunately, many devices can no longer be repaired. However, there are still repair shops that fix mobile phones, washing machines, lawnmowers, etc. – and even if it costs about the same as buying a new device, it still feels good to have done something to make the world a better place.

Returns have become a big problem - many returns are simply burned because the logistics are more expensive than the goods. Especially with clothing, we should research for detailed size specifications so that the clothing also fits. Simply ordering three sizes and of course sending two back is a waste of energy and resources. But other products would not have to be returned if we researched better beforehand whether they meet our expectations.