Hi BenJordan,
Interviews and Group Tasks are looking for you to shine as an individual. I don't know how old you are, but sometimes the best thing to improve people's experience in this area is simply having life experience as they often ask you to call on past situations etc.
With that said, it may not have been all that bad. It could just been that you weren't as confident as the others.
My two recommendations on books would be:
- Great Answers to Tough Interview Questions by Martin John Yate.
- Another good book is Why You?: 101 Interview Questions You'll Never Fear Again by James Read.
They really put in to perspective key parts of any interview. Specifically subliminal body language which you don't ever consider until you've read Martin's book. I once feared interviews too. The good news is they get easier with practice, like anything. The fact you previously attended CTC once before is another advantage for you.. as you know what to improve on :-)