Some common causes of acidity are:

Eating fast food regularly

Addiction to caffeine

Smoking

Too much alcohol consumption

Leaving too much of a gap in-between meals

Some easy remedies: 

Have a glass of lukewarm water every day.

Jaggery (gur), lemon, banana, almonds and yogurt (curd) are all known to give you instant relief from acidity.

Nariyal paani is known to soothe the system if you suffer from acidity.

Boil some mint or basil (tulsi) leaves in water and have a glass of this after meals.

Include bananas, watermelons and cucumbers in your daily diet.

Sucking on a piece of clove is another effective remedy.

Besides, trying to correct the cause, avoid excessive intake of caffeine and alcohol.