There's always some new piece of equipment or new software plug-in we want or must have. In a perfect world, equipment arrives well before the day of the shoot so that we can test it out. We don't however live in a perfect world.
On occasion I've found myself torn between a) pulling an all-nighter to perfect set up technique with new light stands and reflectors or b) "winging it" at the shoot. So far I've mostly resisted the temptation to "wing it-" even when I'm adding back up/redundant equipment to my kit. It's too easy for us to become complacent and think we can work our magic with a new piece of equipment immediately. If we're lucky - that's the case. If we're unlucky, we don't have images from an event. When earlier this year, I decided to "wing it" with a new portable Wolverine media drive, Murphy's Law reigned supreme. I was unable to backup my flash cards on-site. Luckily I had plenty of flash cards and didn't need to reuse them, and I was able to buy more/format them on the way to another shoot.
A confident, poised and professional demeanor keeps everyone relaxed and allows you to deliver your best. Once you've gotten "the money shots," there are almost always opportunities for you to pull out the new equipment and take it for a test drive (just be sure to have a second camera body ready to go in case there's unplanned action that you want to be sure you've captured).
A co-worker once told me about a bumper sticker he'd seen and worked towards as a personal goal: "Of course I don't look busy - I did it right the first time!" When I heard that I immediately thought about how planning is key to getting it right the first time. My take on the bumper sticker was: "Of course it looks easy - I practiced when you weren't looking." More eloquently spoken by Colin Powell, "A dream doesn't become reality through magic; it takes sweat, determination and hard work."