involve TAs in situations which require them to make decisions and act, rather than just "think about things" or just sit. (Even during a lecture or mini-lecture, active listening can be stressed.)
be geared completely to the objectives of the workshop. Objectives should be clearly specified and posted.
provide, as much as possible, for opportunities for interaction and the development of a good relationship between the TAs in attendance -- they learn better. In addition, relationships developed in the workshop can have support value after the training, and may even stimulate the setting up of a mutual helping group.
use content related to needs, interests, and concerns of TAs in your department -- adapt exercises, examples, to closely parallel situations in their work.
balance introduction of new ideas with familiar or comfortable ideas or activities. New knowledge is internalized more readily when it relates to learner's previous knowledge or interest.
provide sequencing. Each activity in the workshop should build from the previous sequence of activities toward the next one, every part fitting into an ordered scheme, that results in attaining the goal of the workshop.
provide opportunities to practice with new ideas/skills/attitudes and to work on the transfer of learning from the workshop to real teaching situations.