In order to understand answer to this question, one should understand what "Shiva" means.
The Vedic literature refers to a minor atmospheric deity, with fearsome powers called Rudra. The Rigveda, for example, has 3 out of 1,028 hymns dedicated to Rudra, and he finds occasional mention in other hymns of the same text.
The term Shiva also appears in the Rigveda, but simply as an epithet, that means "kind, auspicious", one of the adjectives used to describe many different Vedic deities. While fierce ruthless natural phenomenon and storm-related Rudra is feared in the hymns of the Rigveda, the beneficial rains he brings are welcomed as Shiva aspect of him.
This healing, nurturing, life-enabling aspect emerges in the Vedas as Rudra-Shiva, and in post-Vedic literature ultimately as Shiva who combines the destructive and constructive powers, the terrific and the gentle, as the ultimate recycler and rejuvenator of all existence.
So if we treat Shiva as all pervasive God, without any paraphernalia, ie., Thrishula, Damaru, etc, attributed to Shiva or Sankara that we are accustomed with, then meditating upon the all pervasive God can be done in a different way.
Otherwise, if we treat the image of Shiva with paraphernalia, ie., Thrishula, Damaru, etc, the pursuit will meet at a dead end after some time, without further progress.
Let us check the question part, how can I put myself on samadhi/meditation keeping lord shiva in my heart and mind please? . It means pursuing the SPIRITUALITY.
If the OP is desiring to pursue the SPIRITUALITY in a TRUE sense, he/she has to understand the following issues.
- There can be temporary phases in lives of many people, when the desire/itching to attain the GOD will be at peak level, temporarily. It may fade off after some time.
If it is a temporary phase, enjoy the that phase within certain limits, which may recur at a later date, and turn into a serious pursuit. This is a warning because many novices, will be deceived by temporary phases and renounce everything in that phase, and repent later when that phase fades out.
- Meditation is an approach to training the mind to hang on to a SINGLE idea.
A single idea can be an image, a sound, a thought, etc.
- There can be many a pitfall, while performing meditation, like mind getting distracted and engaging in noodling. It is but natural to the mind to get distracted.
The meditator has to bring back the mind to the single idea and start again. According to Sri Ramana Maharshi, it is battle royal, through which mind will slowly get attached to that single idea.
- Finally, that single idea has to be rejected (according to Sri Ramana Maharshi) for attaining the ABSOLUTE BLISS, called SHIVA.