Here is how:

Both you and your girlfriend have to get 20 pieces of paper and make 20 different cards. Each card has an idea on it: you write down things you would like her to do and she does the same with stuff she wants you to do.

There are three kinds of cards: sex, romance and adventure. (If you are doing this with a friend with benefits, drop the latter two.) Each card is two sided. On the outside there is the name of the category, at the inside there is what you would like the other person to do. It should look something like this:

Backside: "Sex"
Inside: "Sex in the elevator"

Each of you has to make 10 sex cards, and choose how you split up romance and adventure cards among the other 10. When you are finished comes the fun part.

Each week, one of you chooses from the cards of the other person. The cards are put into a hat and you have to draw a random card. After drawing, you don't look inside yet. You see what kind of card it is (Sex, Romance, Adventure) and decide whether to keep it or not. If you choose to keep it, you have to fulfill whatever it is on the card. If you drop it, choose another card till you draw a different kind. Put the sex cards that you didn't use back to the other cards.

After a card is drawn, it's out of the game. The one week period between draws can be shortened or extended. Before making the cards, agree with your partner on some rules. Like she shouldn't expect you to take her on a vacation to Thailand, and you shouldn't expect her to go on the street naked.

Here are a few examples for each topic:

Sex:

• Sex in the elevator
• Sex in the changing room
• Sex in your car or at a public place
• Phone sex from two public phones on the street
• Your girlie has to come with you to the shopping center without bras and panties under her clothes
• She has to swallow your cum when doing oral
• Tying your partner to the bed
• You buy her an extreme lingerie which she has to wear 5 times, when you choose to
• She has to let you go anal with her
• She has to drive to you with only a coat on and nothing underneath
• You make a home-video together

Romance:

• A candlelight dinner with your lover in a restaurant which she chooses (you pay)
• A romantic evening at the Opera
• Visiting the theatre
• Having a picnic at the nearby forest
• Visiting a delphinarium
• You rent a 4-star hotel room for the weekend in your city (as long as your financial situation allows it)
• A long weekend at one of the rural areas while visiting some monuments

Adventure:

• Go-kart racing
• Bungee jumping
• Jet-skiing on the local lake
• Parachuting
• Going rock climbing together
• A ride on the biggest roller coaster in the fun park
• Going to an aqua park

Note: I hope I don't have to say that you should only do most of these in a longer relationship, where your partner trusts you totally! The only exception is a friend with benefits relationship in which case it depends on the girl and how adventurous she is.