Being able to give a good reading requires total surrender of self and ego. You have to allow spirit to work through you.
Readers are juggling dual realities and therefore have more balls in the air than someone working soley in the physical. To 'tune in' to someone elses energy field you have to surrender your own physical attachment. It doesn't happen over night because we all have fears, egos, performance anxieties etc. Trust is another big issue with readers. Trust in the energies working with them.
Again it takes time to build trust, respect for the guidance that's given. To do it well, you need to be able to let go of yourself completely. Some readers are only able to do this intermittently and fill the gaps with their own packaging. The reading then becomes contaminated by the readers filters.