Start researching premium car rental as soon as you decide on travel dates--or as soon as you decide you'll be renting a luxury car for a special occasion. While most car rental agencies have a large supply of basic sedans, there will be fewer premium cars available. As the supply dwindles, the price will increase--so your best bet is to book your rental ASAP.
Start your search online. Travel websites like Travelocity.com, Expedia.com and Orbitz.com can give you the best sense of which car rental companies have premium cars available on the dates you need one--and what the price will be.
When you find a good price, check how the car rental agency defines a "premium car." Usually they will give an example of what kind of automobiles fall into that class. Make sure you like the types of cars that agency uses--otherwise, find a different company to rent from and see what their definition of a premium car is.
Check to make sure you're getting the best price if the pricetag matters to you. Once you've identified the best deal from the travel website, go directly to the car rental agency's website to see if they have a better deal. You can go to CurrentCodes.com or NaughtyCodes.com to see if there are any coupons you could apply to the rental. Also check prices available to you through membership of the AARP, AAA, any professional associations you belong to or wholesale shopping clubs like Sam's Club and Costco.