If you can, start your retreat on a day when you can give more hours to formal practice than you expect to be able to do for the rest of the retreat. Make that day special with whatever it takes to create a focused heartfelt intention. This might include chanting, making an offering of dana to a teacher or an organization, or reading a favorite inspirational quote. Something.
Whatever moves you. After several days, many yogis experience a slump when effort lags and doubt ascends. This is the time for a day of determination or maybe just a couple of focused sits to revitalize your momentum and commitment. Each person will have his or her own ways of creating special intention. The key is to experiment and find your own signature and do it.