such a good question and so important. I was the same as you for years constantly ill with coughs and colds from October to March.
Covering up is so important for me, when the weather gets cool I make sure I’m wearing a vest as an extra layer, also making sure my neck, chest and mouth are not exposed when I’m out in the cold. Long jacket/coat, gloves and hat, plus proper shoes and socks to keep my feet dry. Seems so simple but I wasn’t doing those things, I didn’t have a proper coat and my mouth was always exposed.
I now always have Vicks, cough syrup and lemsip in the house for when I feel the first tickle, I make sure I take syrup etc. and stick to taking it regularly until the symptoms are completely gone. Always having it in the house means that when I feel that first tickle in the evening I can handle it straight away rather than just leaving it overnight. Salt water gargle works too, but it’s disgusting.
Food wise I am trying to make a lot of hearty soups. Lemon and water every day, garlic and olive oil as mentioned by someone else. I try to make sure I get some protein, some fats, some carbs, veg every day.
Prioritise sleep, keep layered up at home if house is cold.
I just had my 3rd no cough Christmas and it was great