To determine how best to reduce swelling of the lip or face, it'll be necessary to determine the underlying cause of the swelling in the first place. This can range from anything between physical injury or trauma, a substance allergy or presence of allergens in the environment, insect bites and stings, medical conditions (such as glucagonoma, hives or eczema to name a few...) through to viral infections like Herpes, or nutritional deficiencies.
A common treatment for any type of swelling is to apply a cold or hot compress to the affected area. This is particularly effective for swelling caused by physical injury. A number of different types of compresses are regularly suggested, examples of which are ice cubes wrapped in a towel, a spoon left to chill in the freezer. Hot or warm compresses might also be useful, such as a towel soaked in hot/warm water; heat acts to reduce the accumulation of blood and therefore the swelling, so this type of compress might be particularly useful. Soaking a teabag in hot water and then allowing it to cool before applying to skin is another commonly suggested method.
Rubbing Turmeric or Aloe Vera gel on the affected area is also known help to reduce swelling, especially on the lip area.
If you suspect the swelling might be caused by allergy the best course of action is of course to remove the cause of irritation from your environment before consulting with a doctor or healthcare provider about how best to treat your reaction.
And if you are concerned that the swelling you are experiencing may be related to a viral infection or any other form of medical condition, your doctor is always the best person to seek for advice and treatment.