You've undoubtedly spent months and months slaving over the content, so you'll want a cover that does it justice. Somebody recently told me that the book cover will get a perspective reader's attention, then they'll read the heading. If they're still interested, they'll then read the sub-heading. finally, if they like what they see, they'll then flick through the pages to confirm if it is the book for them. You might have a bestseller in the making, but if it doesn't pass this crucial first step, the chances are it will not be as successful as it could be.
The proof copy is a vital indicator of how your book will look. It is not the finished article, unless of course you're absolutely certain it is what you want. What it is, however, is the final opportunity to make any changes and remove any typos that might not have been picked up in the editing stage.
Take some time to objectively analyse the front cover. Does it leap out at you? Does it interest you? If you cannot switch off your excited mind, then have someone else give you their thoughts. Remember, you might believe you've created a masterpiece, but the reading public might disagree with you. Take their opinions on board. It might be hard hearing criticism or anything they think could be improved, but believe me, it might just save you from even harsher criticism.
More than anything, holding the very first edition of your novel is an amazing feeling. You actually have a tangible product after months of hard work! It might be hard to contain your excitement, but always remember it is there for a reason; to make sure your novel has been thoroughly edited and how it will look on a bookshelf. If you're happy with the proof copy, then go ahead and let your creation loose on the readers!
Best of luck, prospective publisher!