I think a lot of people would be highly surprised at just how innovative they were in the medieval ages tactics/strategies/arms development wise, and indeed just how rapid some of them were when need demanded, as for instance the English tried out no less then three different tactical possibilities against the Scots between Bannockburn and 1337.
Likewise such things as flanking maneuvers, feigned retreats and much more such as holding units in reserve while others pursued a beaten enemy etc had been in widespread use well before then, and so let's hope were able incorporate some of those without making things over complicated.