For any aspiring professional speaker I would strongly urge you to get at least one mentor. Their advice and experience is invaluable and they can bring on an ‘OK’ talk to the levels of ‘Brilliant’.
As a keynote conference speaker I actually have 3 mentors and they each serve a different purpose for me but of equal importance.
The encouraging Tim Luscombe is the mentor who first got me looking at my speech and realising that it could be so much more if I bothered to learn. He remains encouraging with my endeavours and is always on hand to advise on the more practical aspects of professional speaking such as room layout, fee charging and market targeting.
When I obtained the incomparable Alan Stevens as my training mentor I was advised by any speaker I mentioned this to that I had got “Royalty” in speaking circles. After an initial interview Alan agreed to become my mentor and then spent a considerable amount of his own time, over a period of months, working with me. He deconstructed my talk, forced 
me to consider every tiny element of what and how I was orating and, with his help, my talk developed into an inspiring, thought provoking and memorable speech. Alan remains my ‘content’ mentor and under his tutelage (as you never stop learning) my talk continues to evolve and improve.
With my third mentor I struck gold again. W Mitchell is one of the most highly thought of (and highly paid) speakers in America as well as internationally. He counts ex US president Bill Clinton as a friend and graces the Speakers Hall of Fame. His story is jaw-dropping, his fortitude and positivity infectious and his generosity in taking me under his wing is simply out of this world. Mitchell gets me thinking about the more intangible aspects of my speech. What effect do I want from it, how can my talk help other people and what value can I add to anyone 
who hires or listens to me.
And how did I get these 3 amazing mentors?
Simple – I asked them.
I deliberately sought mentors who work and think in a similar vein or genre to myself. They are people I aspire to be like. Not copy or duplicate but to emulate – an important distinction.
My strong advice for any new or novice speaker is to work out where your specialist field is and you want to position your talk. Then look for experienced and respected speakers in that field. Approach them, be prepared to be interviewed by them, showcase yourself and then ask. I am sure, their time allowing, not many would turn you down.