Rid your mind of all concepts of what you think you should be experiencing, and listen to the slightest of sensations anywhere in your body. Don't dismiss anything you feel as 'just normal' feelings. The more you place your awareness on the subtle tingling/vibrations/heat/coolness, whatever you feel, no matter how small and seemingly insignificant, the more you will enjoy it and become more sensitised.
We have become so dense in many ways. It is our sensitivity which needs more fine-tuning, by our acknowledgement. The Reiki energy itself is always there - so long as we are alive!
Although many of my clients report feeling a great deal of heat in their body during treatments, I never feel heat in my hands, unlike many practitioners. Because of this, I used to doubt my ability. With experience, I have come to recognise the lovely, healing energy both in my hands as giver, and in my body as a receiver. Aah! Like sinking into a delicious energy bath. Then my heart fills with gratitude and the experience is heightened even further.
I'm not saying I can expect this every time, but most times, so long as I have put that space aside with intention, it is there. Find also, with self-treatments, your best time to be responsive. And of course, nothing can replace quiet, undisturbed space.
Learn to let go to electrical, twitching responses in your body. Move, go beyond your inhibitions. Those subtle, subtle sensations will soon become charged and active by practice. Be open and accept, go with it, and Reiki will be there for you. It is such a rewarding and exciting journey.