Agreed with the above and i'll expand a bit.

1) DEFINITELY get speed laces for your shoes. Personally I like speed laces with just a simple system.. as opposed to the Yankz system which I hate.
2) If you don't have cycling shoes yet, consider getting triathlon specific shoes. I cycle regularly with my tri shoes and they're just as fine as my old road shoes. These help quicken your transition times since you don't have to mess with a velcro/strap system.
3) Make sure you are training in the R-B-R-B-R format. I've never seen a duathlon (can you post the link to this duathlon?) like this, but if it's what you're doing, you need to practice this type of training on all of your sessions.
4) Learn how to mount and dismount your bike
5) Bring a flag or something that is easily spotted in the transition area. It's EXTREMELY easy to get confused on race day and forget where your stuff is located in relation to the transition exit/entrance
6) What bike are you racing? If it is a road bike, consider a forward seat post that places you farther away from the crank (and therefore using different muscles to cycle) and a pair of aero bars. *WARNING* do this only if you can A) afford it and B) have read enough information to educate and set this up properly.
7) Although it is scary to be in your first competition, DO remember that NO ONE gives a **** about what you are doing,wearing, screwing up, etc. They (and you will be too) will only be focused on what they are doing. So don't feel uncomfortable to get out there and do whatever weird tricks (like putting a giant orange flag in transition area) that will help you.
8) When transition training, always remember that you need to clip your helmet on before you ride, otherwise you will be disqualified. And in the event that you get disqualified (which is only for record keeping anyway and if you are competing athlete), give the ref the finger and keep moving. Your timechip will still yield your time.
9) I'll say it for the 3rd time after these guys.. practice practice practice and repeat.