Why Lord Ganesh is worshipped first before starting any worship or initiating any good activity?

In Hinduism, before starting any Spritual rituals, functions or any activity. Lord Ganesh is worshipped first. Behind this, there is a great hidden science. Many peoples even don't know that Lord Ganesh is the Lord of Mind or can the controller of Psychic powers. Lord Ganesh always provides a positive thought and joyful mind. For performing any activity, hence Lord Ganesh is recalled before starting that activity. On recalling or worshiping, that work is get completed without any hurdle or problem. Because successful completion of any work us completely depends on positive attitude and joyful thought.
Itself name "Ganesh" indicate what it's mean. Meaning of Ganesh is the Chief of group. Can be said master in expert group. As we know mind is Chief controller of human body. Mind controls the body and hence, Organs of the body are Gana or Group and Mind (Maan) is the controller of Gana or Group. Therefore, Mind can be called as Ganesh.
In puranas, it is found that Lord Ganesh was born from Mother Parvati. Mother Parvati had given birth to Lord Ganesh by making idol, collecting her body dirt's and paste of turmeric that she was using to polish that on her body. Then, she give life to Ganesh by using Psychic power. If this story is used to understand properly and any one can get reality of it. Some people's questions me during my preaching, then how Lord Shiva become the father of Ganesh.
Lord Shiva is great yogi, no one can become master in yog without controlling his mind (Maan). Lord Shiva is the controller of Mind by doing continue meditation called Sambhavi mudra. Third eye of Lord Shiva, it self indicate that he has complete control over the mind and has developed well.
Mouse is the vehicle of Lord Ganesh it indicates that Mind is very fast and hurry. It couldn't be controlled by any ordinary people.

Jai Mahakaal.

Why marijuana and belladone generally used to worship Lord Shiva?

In Hindu worship of Lord Shiva, it is generally observed that Marijuana (Ganja or Bhang) and Belladone fruit (Dhatura) which are offered to Lord Shiv as food. These both substance are come under the narcotic act and using in India is illegal. Then some may ask that then why these things are used in worship and also being consumed by some devotees. Yes using of these narcotic materials cause to health problems if these things are taken in excess quantity more than required quantity. According to tantrik and yogic experts considers that consuming Marijuan (Ganja) as smoking or eating Marijuana (Bhang) and Belladone (Dhatura) help to attend deep meditation and Samadhi. As Lord Shiva is the Supreme Yogi and Tantrik, Lord Shiva alway happy to consume and smoke marijuana. With that he also love to eat Belladone.
Hence, typical Shiva Devotees like aghories and Kapaliks alway used to consume Marijuana and Belladone. A chemical compound containing in Marijuana is called Cannabinoid that affect our brain neutons  to think and concentrate on single thought. Due to Cannabinoid, dopamine is get secreted in brain. Then the person feels pleasure, relaxe and euphoria. Therefore, in ancient  india sages were using marijuana to go in deep meditation.