If you are coming to the CR just for several days it is definitely better to book accommodation in advance especially in case you go to Prague or other bigger places during the peak season. It is easier to find any kind of accommodation off-season.
There are several possibilities where to stay. You can start with luxurious hotels in the middle of Prague and popular tourist destinations. But as a young traveler you might prefer something cheaper. There are quite cheap hostels. The price is usually from 10 EUR to 25 EUR. Hostels in the CR are suitable for low-budget travelers who don’t need much comfort. Staff speaks usually English and you can book your bed in advance. You can find more hostels in bigger towns. Most of them are in Prague.
If you look for cheaper accommodation in the Czech Republic you should also check student dormitories. There are always several rooms available for tourists.
Hostels in the CR - http://www.hostels.com/cz.html
Hostels in Prague - http://www.prague-hostels.cz/
Campsites are for those who look for cheap accommodation out of town. You can find campsites almost everywhere. Camps are often situated near ponds or lakes but aren’t very comfortable and well maintained. Campsites are usually open during high season. It means from May till September. Some campsites also offer renting a cottage or bungalow. Prices are not very high. You usually pay less than 100 CZE per night/person but you have to count with other expenditures such as car (in case you have it), dog, tent and operating expenses.
Camping in the nature is possible except from protected landscape areas and National Parks.
Hotels and lodging houses are for those with higher demands. You won´t have any problems to find this kind of accommodation all over the Czech Republic.
It is also possible to find accommodation in private. Local people often offer free rooms for lower prices but of the same quality as hotels.
If you are looking for alternative type of accommodation you might be interested in Hospitality Club or CouchSurfing. This is service for low budget travelers who want to see more then tourist spots. The system is very easy. First of all you have to register and create your profile. As soon as you are done you can start searching for people in destination you want to go to. You contact them and ask for free bed. Everything is for FREE and VOLUNTEER! There are many Czechs registered nowadays so feel free to contact them. We are very friendly and hospitable!
Update: NICM, 02/2014