Previously known for it's laid-back, tiny village character, Tulum nowadays is growing more and more into a popular tourist destination. Nevertheless, it's beaches are by far less crowded than in Cancún or Playa del Carmen, and the town and surrounding with its cenotes and the Sian Ka'an national park might be worth a visit.
Tulum can be divided into three parts: The town / pueblo along the highway 307, the ruins about 2 km north-east of town and the hotel zone about 3 km south-east of town.
Hitching within the city
Hitchhiking from the town to the hotel zone and vice versa is easy and much practiced. You will encounter locals and travellers alike hitchhiking this part of the road 109. From the town, you can walk to the crossing to Cobá and follow the bicycle path southwards. After about 200m, there's a big supermarket to your left. A few meters further, at a smoke shop (or the Captain's bar a bit downstream), there's a popular spot for hitchhiking down to the beach. Here, you'll catch both traffic coming from the Cobá crossing as well as local traffic from the town. Ignore the taxis, you might get a ride easily within a few minutes. Along the hotel zone, any place is good to hitchhike back to town. Another good spot for hitchhiking back is the police post at the junction to the hotel zone and ruins/public beach.
Hitchhiking out is easily achieved along the 307 highway. At both ends of the town, you'll encounter a police post at which traffic slows down. Perfect spots! Make sure you'll be dropped off at the end of town at either side when on transit, otherwise it'll be quite some walk to avoid local traffic. Note that cargo trucks do not drive along the 307 through the city center, but use some small "ring road" around town, meeting/leaving the 307 at the Cobá crossing.
North towards Cobá, Valladolid
At the Cobá crossing of the roads 109 and 307, it should be easy to walk up a few meters to find a hitchhiking spot (with shade) to continue your journey northwards.
Places to avoid
Accommodation and Sleep
For wild camping, enter the beach somewhat at the end of the hotel zone through one of the hotels (see below) and then just walk along the beach until you find some not-yet-developed area. Respect the wildlife, though. Some areas might be closed for public to protect nesting turtles, so do not ever disturb these!
Other useful info
Along the hotel zone, it might seem that entrance to the beach is only permitted when consuming at the various hotels or restaurants that block entrance to the beach. There's a "free" entrance to the beach at Eufemia's (next to Charly's Camping? (need to double check the name)), but in general, just simply walk through the hotel areas straight for the beach.