The best thing to do is to get clear on how you see the marketplace differently and what you offer. This is your viewpoint which, as a thought leader, IS your value proposition.
The best way to determine this is to take your work to the streets.
Start finding ways to work with people in that space both paid (freelance) and unpaid (speaking, writing).
All of these require you to communicate/sell yourself, why you're different and what you can do for them.
Your personal brand = all of those things listed above.
Personal brands exist today because we have universal access to media. Media exists because of the tension that lay between multiple ways of the seeing the world (or an industry).
Thus, you need to see the world in a unique way and share your ideas over and over again, in a useful, generous way, for anyone to feel like you have a personal brand.
Without media, we'd be mostly known as sales people, artists, and entrepreneurs.
And we are those things, but with media, something only big brands once had access to, we now get to act like big brands with big budgets and publicize ourselves all over the internet.
Go sell your services and ideas.
And make your ideas public.
This, today, is part of your value proposition.
The more you do this, the more you will have the personal brand you seek.