Morning exercises, half an hour (at least) walking in the fresh air and before going to bed, vegetables, fruits, apples, especially nuts, low-fat cottage cheese, buckwheat porridge with vegetable oil (any, preferably flaxseed). If possible, less meat, from milk best of all kefir ... I. natural green tea with lemon and a little honey .... And .. smile, gentlemen, smile !!!
Hardening, physical activity, balanced diet, more vitamins in the diet (especially D3), and less anxiety. You can selectively, but it's better all at once) The main thing is without fanaticism!
Hardening, for example, a contrast shower. Plus, proper and balanced nutrition. And I also take Babisan D3. 80% of the population of Russia is deficient in vitamin D and therefore have problems with immunity
Strengthening immunity means strengthening non-specific immunity. Immunity, as you know, is composed not only of immunocompetent cells, but also of the general resistance of organs. General resistance is high due to two factors:
Vitamins to drink, eat meat (optional), salads, berries, fruits and vegetables. Do sports and temper yourself in all sorts of baths (in the shower, too, you can). This is all effective, but you may not notice the result initially because this process is not 1 day and not 1 month
By the way, also fish oil, nuts. Google, everything you need is useful and in moderation <3