Costa Rica is as close to paradise as it gets: the weather is perfect and the diversity of flora and fauna is astounding. No wonder it's becoming the top destination in the world for eco-tourism.
Please take into consideration some of the advice given below and you will have the time of your life. Enjoy your trip!
Avoid San Jose (the capital of Costa Rica)
1) Avoid staying in San Jose. Especially avoid driving there. Many tourists have been targeted. Most of the "horror stories" you hear about happened in San Jose. Why take the risk? A taxi to SJ will cost you the same as to Grecia or Atenas. Note: official airport taxis ("orange") are fairly expensive. It can be as much as $50. If you decide to go this way, make sure that the quoted price is per trip, not per person. If you speak Spanish you should be able to negotiate a price around $25 just outside the terminal with the "red" taxi.
If you want to visit San Jose center (the only part of San Jose that might be worth visiting), go by bus! Stay in the center (around the "pedestrian-only" street). Take only a small sum of money and a camera (umbrella during rain season is a must). There are many policemen in the center, so it's safe during the day time.
As you get further from San Jose, crime rates drop dramatically. Even at the touristy beach towns the crime rate is not as bad as in the capital.
2) Unless you have some experience driving in Central America, avoid driving from the airport, especially if it's dark or raining. Let the hotel / B and B meet you. Many offer free airport pickup or drop-off service. Even if there is a fee, it's typically much less than the official taxi rate.
Hotels and B&Bs in Costa Rica, discounts
3) If your hotel is in the city/town center, bring your earplugs! Costa Ricans have a much higher tolerance for noise. What that means is that if you are staying in the city center there is a good chance that the nearest bar will have loud music all night long. On Saturdays it seems that everyone is having a party. Also avoid hotels that are too close to roads/highways (think motorcycles and huge trucks using engine breaks day and night).
If noise is a big concern for you, email the hotel and ask before you book.
4) Be careful when booking a smaller hotel or B and B. "Private room" almost always means "shared bathroom". If private bathroom is important for you, confirm with the B&B that you're getting one.
5) Some hotels will give you a discount if you pay cash. It doesn't hurt to ask. Note: you can always get a 5-10% discount when paying cash for clothes, shoes, medicine, etc., so don't forget to tell the person attending you that you're paying cash. No discounts for food items though.
6) Do check the hotel reviews on TripAdvisor. The hotel/B&B might look charming on their web site, but be a nightmare in reality. Some of the B&Bs have 5-10 year old pictures from when they were brand new, but now all of the rooms and facilities are in desperate need of renovation.
Driving in Costa Rica
7) Do NOT drive at night. Some roads are very narrow and are poorly marked. There are more drunk drivers on the road at night. In the rain season there is a possibility of a land-slide, fallen rock or tree (happened to us once). Don't take your chances!
8) Don't speed. It's dangerous and a head-ache if you get caught.
9) Don't worry if you're stopped by police. Be nice and patient. If you don't speak Spanish, just show them the papers for your car. Typically they are checking your drivers license, your passport and the papers for the car. If all of that is in order, you'll be on your way in no time.
Do not try to bribe policemen. It's a criminal offence here. If they give you a ticket (usually a $4-10 fine), your rental company will charge you this amount. Then they will pay the ticket themselves. Please re-check this info with your rental company.
If you plan to drive in Costa Rica, please read the Costa Rica Driving article for many useful tips.
Money talk
10) If you plan to drive around a lot and eat in small cafes (called "soda"), you should always have some local cash (aka colones). Same goes for gas stations (called "la bomba"). Please note: most hotels prefer dollars, so don't exchange all the money you brought. Check with your hotels beforehand what they accept. Many smaller hotels (and B&Bs) have a "cash-only" policy.
11) ATMs are a very convenient way to withdraw smaller sums of money. Look for the "Plus" logo at the back of your card. If you have it, you should be able to use your card in virtually any ATM.
Important! Notify your card issuer that you're going to travel to Costa Rica, so that they don't block your card at the worst time possible.
If you are going to use ATMs, remember that if you enter your password incorrectly 3 times, the machine will "eat" the card. You should be able to recover it, but it will take some time (2-4 days). You might not have that time. Be careful, especially if this is the only card you brought.
12) Don't bring $100 or even $50 bills. No one accepts them. You might even have troubles changing those in a bank. 20s are widely accepted. Note: the change will be in colones.