First, after choosing ur henna brand (vatika henna powder, vlcc, godrej nupur, banjaras), put it in a iron vessel and grind beetroot with four to eight cloves and extract the juice and mix with henna powder and make paste like thing. Then pour lemon juice on (1 to 3 tea spoons). Set the paste for minimum one night in the vessel. Stir it occasionally. Then apply it and set it in ur scalp for more than three hours. Wash it alone. Not with any shampoo. Dry ur hair and apply ur normal daily hair oil and wash next day. This method will secure the henna colour for long time. You can add some coffee powder for brown tint. (dont use instant powder.) If u have dry hair you can mix curd or olive oil. But it is not advisable for long lasting colour, because the colour of henna will not set in hair if the paste is oily. Above all, when you are applying henna, make sure that ur scalp is not oily. Shampoo ed hair is recommended. All the best!