The system of chanting that I follow in my classes is the system taught in Sadyojata Veda Gurukula.
It is traditional to chant some s’lokAs, prior to chanting the Gita. The s’lokAs chanted vary a little from one system to another. Please find below what we use in our classes.
You can find the complete Bhagavad Gita s’lokAs here : http://www.gitapress.org/BOOKS/GITA/18/18_Gita.pdf
and here : http://www.gitapress.org/BOOKS/GITA/455/455_Gita_Roman.pdf for download.
pada ccheda anvaya (sandhis) : http://sanskritdocuments.org/all_pdf/gitAanvayasandhivigraha.pdf