There seem to be two main problems when people try to relax. Some people cannot relax because there is a feeling, "I have to be relaxed," and when the feeling of calmness does not come, then a feeling of panic arises. So when we try to do relaxation exercises, it is very important that we do not over-react - whatever happens. Even if we are unable to be calm, just simply accept whatever comes.
The other problem is that when a feeling of relaxation does arise one can get involved with it and consequently attached to it. Happiness and excitement can arise from this relaxation one day but when one comes to do the exercise the next day, one has expectations that a similar feeling should arise. If it does not, again there is a tendency to either panic or become very disappointed. You think - "good feelings arose yesterday, then why not today?" There is a kind of warfare going on with oneself. This is itself an obstacle to relaxation. So the important thing is to have no expectations and to simply accept whatever happens.
The way to relax is to learn how to accept yourself. Let go of any expectations about, "I'm doing this exercise - I should have this result or that result." Instead cultivate the ability to know yourself and be with whatever you are thinking or feeling. Making friends with yourself without fighting yourself - that is the way to find relaxation very easily. To someone whose mind is really mature, they can be very happy wherever they are, whatever happens because they have learned to accept themselves and whatever they experience.
It's so important to accept whatever we are thinking or feeling without judgment. I know that is radical advice. It is also what works if we want to cultivate a relaxed and liberated mind. Just begin. Whatever you are thinking and feeling right now, right this very minute, accept. Even if you don't like it, accept it. Even if you have already judged it, don't judge the judgment. Non-judgment can only happen in the moment and we can do that at any point. Once you have accepted yourself completely, if only for a nano-second, then you know how to do it. Then your aspiration is simply to increase your percentages! Every time you are aware of attachments or expectations, just accept yourself in the moment. I promise you that your peace of mind and happiness will only increase!