There is no one most valuable topic. There are a series of critical topics all of which need to be covered.

Tenacity

be consistent with your marketing method of choice....and that would depend on whether you focus on listings or buyers.... two different methods...

So many good topics already suggested and likely many more that will follow for a series in your program that explores real life now that you have your real estate license.  Good luck.  How do you plan to attract and engage these new agents?

Generating business, executive a business plan.  A realistic business plan.

All the options for prospecting!

goal setting

How to find clients

Understanding and writing transactional documents. Most new agents do not understand contract writing because they don't get a lot of training. I know in my state it's only 6 hours and that is nowhere near sufficient.

Cut through all the bologna & let's talk about the actions they should take that are a direct line to making money. A lot of time is wasted on everything but that. I train my team members on how to be successful &  when they commit to doing what I say they succeed!

Scripts, prospecting, contracts and documents, technology. Hard to say!

Have at least $20,000 in reserves. 

lead gen - if you get good enough at that - you can hire everything else.

Contracts and negotiating. 

lead gen systems.

I think there are many that will be on the top of my list. What to expect. What is expected of them. How to answer the hone. How to write a contract. How to talk to another agent. How and when to seek help. Who to work for and why and mandatory mentoring

Prospecting

I am putting together a training manual for my team. Everything is important and will be covered. The most important thing: How to find clients. Without it you have no business.

Lead generation

Budgeting, marketing plans, business plans, how to avoid the piranhas that feed off of new agents with branded give aways.  I'd also include how to generate your own leads so you don't have to (or feel compelled to) buy them from zillow/realtor/homes/nextdoor/idealestate/and so on and so forth.

Let's Get Personal--unless you can connect with people whether online or in person, you will not succeed in real estate.  This is a People Business.

Silence all the non-sense.

Without a business plan the newbie is simply another smiley face in the sea of smiley faces.

Without a business plan, the newbie is practicing accidental real estate.

Without a business plan, a newbie in in a race between their saving balance and their first accident.

With a business plan. the newbie knows what their second step is.

Of course. the business plan should have been completed BEFORE entering real estate school. Once in the jaws of a broker, the newbie will be robbed of $12,000, blamed for their failure and owe the IRS for the sale they did make. 

Hunt. gather, and delegate with grace

1. How to build a successful and sustainable business.

2.  How to build a successful and sustainable business.

3. How to build a successful and sustainable business.

John,

I am in agreement with Nina Hollander .  A

Human Nature....it all boils down to that

Be a good listener. 

Most every "newbie" I've know could include a lesson on how to interact with other agents, especially those of competing agencies.

How to stay in compliance

In my previous career- I was a training manager and trainer for Wall Street firms (institutional end of the business- Investment Banking, Hedge Funds, Exchanges, etc. ). Now that I am in real estate as an agent- it's a very different audience with very different needs. There is no 1 important topic. Training for new agents should be holstic. I do advise new agents that want to focus solely in sales to have 2 years worth of expenses saved (we have nearly 30k agents in Manhattan and only about 11-12k sales per year). Agents can make quicker money in rentals (and earn a nice living) but it's difficult to carve out a reputation the same way you can in sales. While my firm does have formal trainings- they are always working to improve the process- and I will likely be consulted having a substantial background designing training programs (provided it doesn't distract from my production I am open to it).

training sessions and how to obtain and keep clients

Focus and self discipline 

Everything is important.

I've done that. 

Now, NO MORE NEW AGENTS. 

How to be professional and that includes dressing the part.  I saw an agent showing homes in cut off shorts, flip flops and a craft beer tee-shirt.

Lead generation is the most important aspect of our business.

Every point is valuable - no shortcuts in training new agents from forms, to etiquette, effective communication, treating it as a business, the importance of ethical behavior and avoid expecting immediate success, it may take a while.