The larger tour busses are quite comfortable and clean. They have air conditioning that can get VERY COLD. Remember to take a jacket with you. Most likely you will need it.
When riding a bus some can get very noisy. Dominicans do like to listen to their music loud and they think everyone likes it that way also.
When riding a local bus or Guagua they can get loud and are many times dirty and crowded. Many of the smaller guaguas or busses do not have air conditioning so you have to open the windows. They can make many stops along the route. You could even be riding with a box of chickens in the back! So relax and try and enjoy the experience. Nothing much else you can do except get upset which does not help or get off the bus. Remember, when stops are made watch for a might-be thief putting his hand into the window to take what you have when you are not paying attention and cannot make chase. It happens often so be aware.
Driving while drinking is not permitted. The country has been cracking down on drinking and driving so be aware. If you are in a wreck or do a traffic no-no drunk you'll be in big trouble. Even though they say no drinking and driving many people do and the police really do not pay much attention unless you look like you are doing something wrong or make a mistake.
I strongly suggest, especially if you are not familiar with the country, get a taxi, Do Not rent a car (or use public transportation) to travel around the country. Driving is not easy here. If you get in any type of accident you may not be able to leave the country until it is resolved. Remember, the police do not get paid much money (in general, basic pay can be less than $200 US Dollars a month). This is not enough to raise a family so many of the police do look for tips (regalas). Some spot a tourist and will pull them over and ask for money or they will give you a ticket or take you to jail. It is up to you, but I suggest try not to give money or give a small amount just to get out of the problem. Do not let them see how much money you have. Do not get too aggressive in your argument with them (a little arguing is expected). Many say to make a copy of your drivers license and give this to them instead of the original. Again I suggest, just to be safe, use a taxi. *note- I do not know about the police asking for a tip first hand. This is only what I have been told by other Expats and Dominicans alike. I have never had a problem with this in my years in the country. I do always use a taxi or public transportation.
When taking a taxi always ask before hand what the fare will be. This way you can decide then whether to take that car or not. Once you have taken the ride you have no choice but to pay what he asks.
When using public transportation be aware of your surroundings. Watch who is close to you, bumping into you or making loud noises can be to distract you into not paying attention to the hand reaching into your pocket or worse.
The Public cars are convenient and inexpensive. I strongly suggest that you do not use Public cars at night. Best to take a taxi. Official registered public cars will have an ID badge in the car with the drivers picture and their identity number.
Have the money to pay the driver or bus attendant in your hand or in a convenient place away from your other monies. This way you will not be showing how much money you have to all the passengers.
Always try and smile and be nice to the driver. Tell them thank you. If possible, in a public car, say the drivers name when speaking to him. This way they know you know who they are.
Look in the car first. If you don't like the look of the driver or passengers (most likely you won't like the look of the car, but this is normal. Can't be too choosy with this point) don't get it. Wait for the next car to pass. The Dominicans do this so you can also. It is better to be safe than sorry. Follow your feelings and instincts.
Do not leave your purse or belongings on the seat near you if your windows are down. Keep them on the floor between your feet with the strap held or wrapped around your leg. Grab and runs are very common.
When talking on your cell phone use caution if the window is down. I know many people that have had their phones torn from their hands while talking from someone in the street or a motorbike passing by.