You should clean your instrument after every use. It is extremely important also in connection with hygiene as well as to keep the recorder in good condition.
Plastic recorders can be cleaned with warm tap water. Before doing so, take it apart and then make sure that all parts are totally dry before using it again. 
In case of wooden recorders, after taking it apart, clean it carefully with a piace of cloth.
It can happen that the saliva congests the pipe during use. You can decrease the number of congestions if you preheat your instrument with your hand before starting to play.
If there are too much moisture in the mouth piece, you should block the pipe with your pointer and blow the pipe with one powerful blow. This method should remove the moisture from the head joint down to the middle joint. After you have finsihed playing, you should clean the moisture from the middle joint as well with one of the above mentioned techniques.