Well done on getting some calls lined up!
Now, in terms of at the end of/after a call make sure you:
1) Write a thank you message within 24 hours
2) At the of the call, if they have not offered a referral then try to play "tag" and get put in touch with a 2nd person (i.e. at the office you're interested in, of a closer background to yourself, in a practice you're interestedin, etc.
3) Finally, a few days before you apply, send them an email essentially saying "thanks for your time x weeks/months ago, just wanted to let you know I'm applying in a few days. If you have any advice I'd love to hear it, otherwise thanks again for your time"
This is your final attempt at pulling out a referral!
Note: If you know the person well (close friend, etc.), it may be worth the gamble to just ask directly (use your own discretion here)
In terms of networking tactics:
a) Reach out to people in your network
b) Reach out to people once removed from your network
c) Reach out to people with a similar backgorund to you (i.e. same alma mater, same hometown, same career switch, etc.)
d) Tailor a message to them specifically both showing interest in them and their journey and demonstrating that you have done your research and could be a valuable hire
e) Play "tag" across calls you get so that you can work your way towards the company/office/role you want
f) Leave a strong impression - i.e. don't ask "basic questions". Rather, demonstrate your ability/intelligence by asking smart questions, carrying a natural conversation, showing genuine interest, etc.