My quick and easy henna paste only requires the following; henna powder, lemon juice, and essential oil. Lemon juice bottled or fresh squeezed, either one works just fine. For essential oils I like to use eucalyptus (widely available and inexpensive), lavender (widely available, moderate cost), and tea tree oil (widely available but crazy expensive at times). You can add water or sugar to your paste if you like. I only add sugar when I am using a henna that is not naturally stringy. I typically use water when I mix henna from Morocco.
Please remember the idea is not to get perfect measurements, or exact measurements, that recipe does not exist. The idea is to get the right texture/consistency. The ideal consistency is toothpaste, mashed potatoes, or smooth peanut butter. If your henna paste is too thick and dry use more liquid. Too runny? Add more powder.