Text classification: Choosing training and testing set for each category
The most commonly used option is 2/3rd of the data as training and 1/3rd as testing sets respectively. What kind of software or tool are you using for this categorization process? For your classifier to work efficiently at the end of all the hard work, have you considered cross validating it using a multiple fold cross validation before using and assigning the training and testing sets? As in for the skewed data categories, try finding instances for the classes/ categories which have fewer samples (~10%).