How best to accelerate vast accumulation of merits?
Ways to earn merits:


Practice the Buddha's teaching. 
Practice Dana.
Practice daily meditation and share the merits with all beings.
Support the Sangha or better yet, become a Bhikkhu/Bhikkhuni.


With every wholesome deed one gets closer to Nibbana. 

With every unwholesome deed one gains distance to Nibbana.