The first and foremost thing that one needs to be keep in mind before performing any puja is that the devotee should take a bath.

The first and foremost thing that one needs to be keep in mind before performing any puja is that the devotee should take a bath.

Never put tulsi (basil) leaves on the shivling . Always offer only Bael leaves.
When offering milk to the shivling make sure that you never use pasteurized or packet milk and make sure you always use ice cold milk.
Never offer coconut water as an offering to the shivling, although you can offer coconuts.
Although many fruits can be offered but the most common fruit that is offered to the shivling on all major festivals is Bael (wood apple) as it signifies longevity.

The shivling should be first offered Panchamrit, which is a mixture of milk, yogurt, saffron, sugar/honey and pure ghee.
It is believed that the shivling and the idol of Lord Shiva should only be offered white flowers because Lord Shiva is said to be especially fond of flowers that are white in colour.

Never offer kewda and champa flowers as they are said to be cursed by Lord Shiva
The devotees can put a tilak of sandalwood paste on the shivling.

Never use a kumkum tilak for the shivling, although the devotees can use it for the idols of Maa Parvati and Lord Ganesha.

The devotees should never consume whatever they have offered to the shivling as it is not considered good.
Always remember if you keep a shivling at home it should be accompanied by a jaldhara. If the shivling is worshipped without the jaldhara it attracts negative energies.

There are many other beliefs that are suggested by various experts and religious figures but these are the main things that should be kept in mind while worshipping the shivling.
Om Namah Shivaya!!!