The aim of this study is to put together the basic concepts of mechanics on drill string which are related to directional drilling, thus finding a less complicated and more economical way for drilling directional wells. Slick bottom hole assembly, which has no stabilizers attached, and single stabilizer bottom hole assembly are analyzed through previously derived formulas gathered from the literature that are rearranged for this study. An actual directional well is re-drilled theoretically with a slick assembly and a computer program is assembled for calculating the side force and direction of the well for single stabilizer assembly. Influence of controllable variables on drilling tendency is investigated and reported. The study will be useful for well trajectory and drill string design in accordance with the drilling phase. Also, by using available data from the offset wells, the drilling engineer can back-calculate the formation anisotropy index that is often used for optimizing well trajectories and predicting drilling tendency on new wells in similar drilling conditions which is also shown throughout the study.