The Sabbasava sutta (MN 2) on appropriate attention doesn’t mean letting go of all thoughts, it is more selective than that, it means letting go of sense impressions or thoughts that are unfit for attention, and holding onto those sense impressions and thoughts that are fit for attention. There are seven methods, six strategies for abandoning and one for developing. The specific fermentations to be abandoned by each strategy and the factors to be developed are described in the sutta. Abandoning and developing is the basic means of progress along the path, and the same process is found in right effort and also under the fourth foundation of mindfulness (MN 10), so it is the fundamental means of transformation in the path.
MN2 should be studied in conjunction with SN 46.51 as it gives insight into the simple psychological working of abandoning and developing.
An overview of the process under the heading of the path factor of right effort:
The strategies in MN 2 are based on the momentary act of attention (manasikara), which is a factor in all states of consciousness and it is the mind’s first encounter with the object. Whether it is appropriate or inappropriate attention is a choice to be made at that encounter, so mindfulness of what is presenting before the mind is necessary. Everything that we do involves a decision that can be towards appropriate or inappropriate attention. In this way experience can be used to lead either towards suffering, or towards freedom from suffering.