When constructing triangles, you need either three side lengths (SSS), two sides and the included angle (SAS) or two angles and a side (ASA or AAS). These sets of information ensure you can form a unique triangle. If you're given two sides and a non-included angle (SSA), the triangle might not be unique or even possible. Remember, the sum of the angles in any triangle will always be 180 degrees, which helps in checking the validity of given angle measures.