With every graduating generation of shinigami there are some who excel in strength, and there are some who excel in finesse. Some of them are best at close combat, and some who prefer to have distance between them and their opponent. Also with every generation there are a few who prefer to use the core of their being in battle, their brain. Thirteenth division focuses on training shinigami to use their head in combat so as to maximize their strengths and minimize the prevalence of their weaknesses.
By doing this members of thirteenth are effectively trained into becoming formidable foes in combat not because of a specific discipline, but because of how they think on the battle field. Members of thirteenth are shown and trained not only how to use their surroundings to their benefit, but also how to manipulate their opponent in a sub-conscious manner.
To a member of the thirteenth division a fight whether it is a one on one fight or a large scale war is always seen as an elegant game of chess with each move made by the member being a balance of both spontaneous and calculated.
During combat with a team, the trained 13th division member can quickly asses their teammate’s strengths and weaknesses and start forming a strategy that would increase their team’s chances of winning. Hence why the division motto is "Just Trust Us". It is meant more to as a promise to fellow teammembers that even though the plan may seem outrageous, as long they are willing to cooperate, the team will retain its a strong chances of success.
Most importantly though above the tactics side of combat, is how one uses the skills they have. Before a member of the 13th can form any sort of plan, they have to know what they are capable of. Members not only train thier mind and body for war, but also how to invent and reuse old tricks in new ways.