If you'd like to coach yourself, two GREAT books I can recommend are:
Airline Pilot Interviews: How You Can Succeed in Getting Hired
by Irv Jasinski
Worked for me
It explains everything going on behind the interview!! Another great book is:
Great Answers To Tough Interview Questions, Fifth Edition
by Martin John Yate
So when they ask you a tough question, what are they really looking for? A bit of effort here can work wonders!! Some great examples given.
Before I read these books, I would have hung myself with all the rope they gave me!! It's all about knowing how the game works. Turning everything into a positive.
So many people focus too much on the Tech, but prepping your HR answers is just as important.
Good luck!