First of all, get plenty of rest and drink plenty of water. If you feel unnaturally cold, do not attempt to warm yourself up, as an unnatural cold feeling is one of the first signs of a fever. Eat chicken soup and hot drinks (non-caffeinated), raw garlic or garlic powder (for the allicin), as well as plenty of Vitamin C, Vitamin B6, and Zinc.
For a fever, put a cold wet towel on the forehead, as well as drinking plenty of cold water. Take Acetaminophen (aka Paracetamol) as instructed by the medicine packaging. If fever still does not go down, seek medical attention. Do not give aspirin to a child.
For a sore throat, you can gargle saltwater or take a cough drop. After your sickness is cured, dispose of your old toothbrush or deep-clean it. Wash your sheets, especially if you share your bed.
For mucus, drink plenty of water. Water vapor works, but you need to use it in a small room or use a water mister with a mask.
If you need to go out, put on a disposable surgical mask. If you anticipate a lot of content, put on gloves.