Okay, you've just flown in to Cancun, had booked a rental car and picked it up at the airport.  What do you do now?

Driving to Tulum from Cancun is very, very easy.  But a couple tips can help you on your way.

First thing, release the parking brake in the car before you drive away (I speak from experience)!

Now, follow the signs for 307 SOUTH to Playa del Carmen or Tulum.  This is the road you will be on for pretty much the entire trip.  It's a straight shot.

It should take about an hour and a half to get to Tulum in normal traffic.  Once there, you will pass an entrance to the Tulum Mayan Ruins (on the left).  Shortly after, you will be in Tulum.  At the intersection with a San Francisco supermarket on the right and a 7-11 on the left, make a left turn, heading toward the ocean.  This will take you to the beach road.

After about 3km you will reach a T-intersection for the beach road.  Make a right turn and follow the road down to your respective hotel.

Here is a Google Map of the Tulum area for reference.

A few driving tips for the roads of Mexico:

• get the rental car insurance for collision damage waiver and liability.  Even if your credit card provides coverage in Mexico, it will likely be for reimbursement and you will need to pay any damages in cash before you can leave the country.
• check out the car rental FAQ thread on tulum.info.  Useful info to know.
• a road sign that looks like a few little pyramids lined up means slow down and watch for an upcoming speed bump.  These speed bumps are nasty and you don't want them to catch you by surprise.
• if someone is tail gating you or driving fast and flashes their lights, keep driving but move half-way onto the shoulder on the right to give them room to pass.  This is common curtesy for passing in Mexico.
• if someone is pulled all the way onto the right shoulder, but is stopped with a left turn signal on, they may be waiting for traffic to clear for a complete left turn.  You may not see this too much, but again it's curtesy to keep from blocking traffic.

It actually a very easy drive!  Just obey the rules of the road and posted speed limits.