Reflect on the Triple Gem. Perhaps for a whole period, reflect on the dependent arising nature of your understanding. This is the classic way to increase confidence in the Triple Gem. Reflect on any benefits that you've received from the practice. Ask yourself how it came to be and trace it back to the Sangha and the Dhamma and where did that come from; all the way back to the Buddha.
Unless you reflect on the Triple Gem, it's difficult to increase faith in them. Unless you reflect on the benefits that you gain from the Dhamma, the confidence in the Dhamma does not increase as quickly. So classic thing is to reflect on the Dhamma and reflect on what it has done for you. How you are using it in your life. How it has helped you to grow and then reflect on how it came to be.