God can appear with form and without form. But during your meditation, it is best to think of the Supreme as a human being.
The beginner should always meditate on the personal God. Otherwise, if you try to see God in His impersonal aspect, you will be confused by His immensity. So start with the personal God and from there you can go to the impersonal God.
Today you may be a beginner in the spiritual life, but do not feel that you will always be a beginner. At one time everybody was a beginner. If you practise concentration and meditation regularly, if you are really sincere in your spiritual search, then you are bound to make progress.
The important thing is not to be discouraged. God-realisation does not come overnight. If you meditate regularly and devotedly, if you can cry for God like a child cries for his mother, then you will not have to run to the goal. No, the goal will come and stand right in front of you and claim you as its own, very own.