There are so many albergues in Spain (more than 500!)…let yourself go with your impulses, your desires, your encounters…Don’t rely on preconceived ideas about your state of fatigue, your strength, the weather…
The only exceptions, perhaps, are the big towns (Pamplona, Burgos, Leon…) but wait to be in the vicinity! Also, better book at the very busy period of San Fermines Fiestas in Pamplona from July the 6th to 14th
Know, however, that if you want to make reservations, very many lodgings now accept them.