Answer
First of all, you need to read Srila Prabhupada’s books. Only then will you understand what is actually before you when you chant Hare Krishna Hare Krishna Krishna Krishna. What is this sound? What is its value? At least theoretically, you must understand this.
That is the first step.
Secondly, you should understand why you are chanting. What are the results of chanting? And what is the process to achieve those results?
These three types of knowledge are essential:
Who or what is the Holy Name
Why we are chanting
What is the proper process of chanting
This is sambandha, abhidheya, and prayojana in the practice of nāma-japa. You must hear this from guru, sadhu, and shastra.
You should clearly know:
What this sound is
Why you are chanting
How you should chant
When you understand these, enthusiasm will come automatically.
For example, if I give you a large plate of mahāprasādam with many varieties, will you feel enthusiastic or drowsy? Of course, enthusiastic—because you have realization and firm belief that it will give you happiness.
But with the Holy Name, that full belief is not yet there. Still, the Holy Name is also ānanda, just like mahāprasādam. The difference is that you lack realization.
So what should you do?
You must apply your mind—do manana (deep reflection). Read the philosophy of Krishna consciousness and practice it. Gradually, realization will come. Then you will experience:
Sat (eternal nature)
Chit (knowledge)
Ānanda (bliss)
You will realize that pure knowledge is coming from the Holy Name.
In fact, even if someone sincerely chants and hears attentively, without reading shastra, all scriptural knowledge can awaken within them—because that sound contains everything. All knowledge and all bliss are present in the Holy Name.
Therefore, first read Srila Prabhupada’s books and understand this properly.
You can focus on this subject specifically. There is a book called Nama, which contains many of Prabhupada’s quotes on the Holy Name. Read it again and again. Hear it repeatedly.
Then you will know what you are doing.
Right now, you are chanting without proper understanding—perhaps because someone said, “Chanting is good.” So you chant, but feel drowsy.
All the answers to this are already available in Srila Prabhupada’s books.