Monday is the most auspicious day and Shravan month is the most auspicious month for the worship of Lord Shiva. We should offer bel patr, dhatura (favorite flower of Lord Shiv) to Lord Shiva and then conduct Abhishekam. Without Abhishekam, the worship of Lord Shiva is incomplete. You can use milk, water, holy river water like the Narmada, Ganga.