We usually put tickets on sale for the league games at the Camp Nou on the beginning of the football season.
However, in both football and basketball matches, the Club works with the "Seient Lliure" system, so members subscribed can "free" their seats as the match is closer, being the 48h prior to the match the most active deadline, thus leaving many more seats on sale. Therefore we recommend that you follow by accessing to the match until you find free seats.
On the other hand, you need to know that for matches with a high demand of tickets, it is too difficult to find seats together. Our tip: buy tickets where you have visual contact with your companion, and share the time in the areas of restoration during the match half-time.