dhyāyan bhagavato rūpaṁ
The yogic principles of meditation are clearly explained here. One has to fix one’s mind upon the form of the Supreme Personality of Godhead without diversion to any other objective. It is not that one can meditate or concentrate on an impersonal objective. To try to do so is simply a waste of time, for it is unnecessarily troublesome, as explained in Bhagavad-gītā.