What should someone who wants to go on this magic path focus on first?

All magick relies on your ability to communicate with the spirits. Therefore meditation is the first key. It helps open your hearing, ability to feel energy different than your own and to help open your vision. Other than that, you should make a practice of knowing the LBRP or the Banishing rituals of the Left Hand Path. You can search the forum for banishing mantras as well already posted.