Profession
The ruler of the 10th or MC is one significator among many that can point to one's likely professional focus. Whatever house the MC ruler is in can shape the type of work: 1st -- spokesperson, receptionist, 3rd -- writing, sales, 7th -- broker, agent, counselor, etc. Strong or significant aspect patterns will tend to manifest in many areas of ones life, particularly in the work one does. Since the planets represent energy they will tend to be stronger than signs (quality of expression). Houses (areas of expression) will often be influential. Any general rule will often be found to be broken more than followed but I would rate the factors (from strongest to weakest) as: Planetary patterns, houses, rulerships for combining planets and houses, and lastly signs. Dave.