Meditate in a clean and quiet place. Try to take a shower before you meditate. If you don't have time to take a shower or bath, then wash your hands and face.
Water has a very pure consciousness.
When you take a shower, the subtle physical vibrations of the water neutralize a great deal of the negative energy that your body accumulates. Try to avoid eating before you meditate. If you eat too much before a meditation session, you will find it hard difficult to meditate. Instead of meditating on peace, light and bliss, you will meditate on pasta. If you are hungry, then drink some fruit juice or eat something light.