One of the first things that you will learn in your high school or college chemistry class is that an acid always neutralizes a base, and a base always neutralizes an acid. Acids include vinegar, muriatic and citric fruits like lemons, and will turn a litmus paper red. Bases include sodium hydroxide, calcium hydroxide, ammonia water and many bleaches, and will turn litmus paper blue. Although neutralizing acids and bases is simple in theory, you have to be extremely careful when working with chemicals in order to prevent serious burns.
Put on a pair of protective gloves to prevent any skin burns. This step should be taken whenever working with chemicals. You may also want to put on protective eyewear and a face mask, depending on what kind of chemicals you're working with.
Pour baking soda directly onto any acid spill. This will neutralize light acids like vinegar or even strong, dangerous acids like muriatic and sulphuric acids. Douse the entire affected area with the baking soda (sodium bicarbonate, NaHCO3) to neutralize the acid. Wash the spilled area thoroughly with water, then dry with paper towel.
Squeeze an entire lemon onto a base spill if it is a small spill. For larger spills, pour vinegar directly onto the base spill. The citric or acetic acid will neutralize any base spill. Once neutralized, douse in water and dry with paper towel.
Never handle strong acids or bases without the presence of a teacher, chemist or professional in the field of the chemicals you're using.