Sending energy without knowing about the actual blockage is fine. It's the message you send with the visualization of the energy that is more important.
You should send a message like "This pure universal energy joins with XXXX and heals YYY and pain (or ZZZ) is completely gone". Keep it totally positive and confident. It will work.
Master Lin talks about the differences in sensitivity to energy of different people. Saying that some peoples blockages are completely gone, when they start to relax, or when he says you channels' are open. Other people require swordfingers and similar techniques to clear blockages. Others still require multi-mode, using massage, medicine, nutrition, and multiple SFQ sessions before the blockages are completely open.
The differences are not only a reflection on your own ability, but on the receptiveness of the person you trying to help.
You best help is to send confident positive messages from a place of love. You may have to do the many times, but know that each time you do it, you are doing good. 
Remember if Master Lin has to help people seceral times, us beginners shouldn't become discouraged if everything we do isn't complete during a single session. We all improve with practice. You not as good now as you will be in 10 years.
You are perfection.
Iam2 
