Exchange larger bills for smaller bills, in $1 and $5 denominations. The amount you need will vary depending on how much you plan to tip and the length of your stay.
Give the valet $2 when you drop off your car and give him your keys. If you have a nicer car that you would like to have parked where you can see it or in a safer spot, you might want to tip more upfront as an incentive.
Say thank you to the valet who takes your car. Remember that she is performing a service for you and if you want her to take good care of your vehicle, a "thank you" can go a long way.
Give the valet another gratuity when he delivers your car safely. It is customary to match the amount you gave when you dropped off the car.
Increase your final gratuity if you have been coming and going a lot throughout the day. Typically, the valet will refuse tips for in's and out's throughout the day, so a larger final tip makes up for all the extra service
Thank the valet again for her service, especially if you will be returning to the hotel or restaurant.
