When you apply and don't draw a tag you are awarded a point instead. Tags are limited, so those with more preference points get the tags first. You can apply for just a preference point and not the tag. It would be a good idea to do so. You would need to send in the cost of the tag, $334 when you apply. You then get a refund in June for the total less $28.
The code to use for a preference point for deer is D-P-999-99-P.
http://wildlife.state.co.us/ShopDOW/AppsAndLicenses/