Mindfulness of Breathing:
Signs of concentrated states:
Therefore, use the breath as access, then switch to pleasant physical sensation such as smile, hands, heat and stay focused on that pleasant sensation. Create a positive feedback loop of pleasure sensation. Maintaining attention in this way will lead to entering the first jhāna - the others should follow in sequence. Do not "reach for jhāna" as craving will create a hindrance.
Leigh recommended doing half of sitting practice in jhāna and the other half as insight meditation.