I will mention (again) the Kalavinka Press series. http://www.kalavinka.com/
Excepting the two meditation books & the Stories volume, everything there is seminal and clear and focused on the bodhisattva path.
The "Friendly Letter" of Nagarjuna was a favored primer for aspiring bodhisattvas in India long ago - so why not study it first? Kalavinka's edition has three translations - all older than any Tibetan version.
I am fond of Vasubandhu's work on bodhichitta and N.'s Bodhisambhara Shastra
which latter Dharmamitra has in two versions: abridged & a full commentary by Bhikshu Vasitva.
Since Nagarjuna is often thought of as the "founder" of Mahayana his shorter texts should be at the top of any list.