Last year was my first time showing a rabbit, but I got marked down because I didn't practice with her. I had no help from the adviser for bunnies where I go to school, so I did not know what to do. What are the important things to know and do when showing a rabbit?
Depending on where you are doing showmanship (ARBA, 4-H, FFA, etc) there will be some sort of reference regarding what is tested. You will want to find that reference and be prepared to do the things that are asked. This means that both you know how to do them and your rabbit will cooperate. This takes practice. For instance, a common request when I was in 4-H showmanship was demonstrate how to sex your rabbit and identify the sex organs. This involves knowing how to turn your rabbit over and pop out the genitalia, being able to identify the parts of the genitalia, being able to do so without visible embarrassment, laughing or blushing, and your rabbit cooperating with the procedure. You also need to teach your rabbit to sit calmly on the table even with other rabbits nearby. Other tasks I remember that took a lot of training with my rabbit were examining the nails and ears and showing the ear tattoo.
Another thing to remember for showmanship is that you and your rabbit should be clean and neat. You should dress both nicely and in colors that compliment your rabbit. You will want to make sure that your hair doesn't fall in your face or on your rabbit, as that can be distracting to the judges if not to you.
You can learn a lot about showmanship from other people doing showmanship even (and maybe particularly) if they aren't doing rabbit showmanship. If you are in the US, your county extension service probably has some free or low cost resources on doing showmanship, although they may not be for rabbits, they would still be useful.