Set up some robot design/build sessions to improve your team's skills in those areas. If you have a good builder on your team, this is a great way for him/her to share those skills. If you need some outside help, you can contact a veteran team – the Inventioneers are always available for this!
Check your local bookstore or the web for books about NXT robots. We like Eric Wang’s book Engineering with LEGO Bricks and Robolab (http://www.collegehousebooks.com/lego_bricks_3.htm ). Even if you are not using Robolab software (this is one of the two programming languages permitted by FLL – the other is the software that comes with the Mindstorms kit - NXT G. - we have 8 years of experience using Robolab and are happy to provide training workshops), the book has some good building exercises to try.
Also, check out internet sources for other building tips. Check out Youtube videos of other teams and other year’s challenges. These cool robots might spark creative ideas in your team.