Tajic is a very powerful creature that can be well utilized in a proper deck. As of now you may find him in the following two decks.
This card just begs to be played in an aggro deck, and since it is made for the Boros guild, it perfectly fits the Path of Mettle gameplan. You can also add Kwende and a few other creatures with First Strike that will gain Double Strike as a result. In combination with Aurelia, Exemplar of Justice and Heroic Reinforcements it could become one of the most dangerous decks in the meta.
The Jeskai variant is very similar to the Boros deck, but here you could add a few blue counterspells just to keep things going and prevent the possible board clears from your opponent's side.