Letting go, in practical terms, has its basis in mindfulness. It starts with stepping back - from the thoughts, from the feelings, from the reactions ... and just noticing them. 

Try this:

Think of the problem or issue, notice the thoughts you are having about it (literally say to yourself "I am having the thought that ..."). Say this to yourself many times out aloud if you can. Say it about all the thoughts you are having around this issue. Then start the sentence with "I notice I am having the thought that ..." or "I notice I am having the feeling of ..."

Notice how you become the observer of the thoughts and feelings. you are narrating what is happening in the mind and in the body. This is mindfulness. When you find yourself attaching to the thoughts and chasing them, use these sentence starters to step back from attaching.

This process is not about discarding the thoughts and feelings (that will happen eventually) - rather it is about acknowledging them so they do not grow in their intensity - which is what happens when we avoid thoughts and feelings. 
It's also about not becoming stuck to thoughts and feelings - not fusing with them. Its about stepping back from them, getting distance from them and observing them from that distance. Its about perspective. 

Stepping back allows other perspectives to come into play too; alternatives, other possibilities, creativity and balance. 

From here we are able to focus on creating change and a new experience for ourselves - rather than staying stuck with the old out of fear and lack of alternatives.