Rulers and dispositors
Every sign has a planet in charge, and following the chain tells you who really runs the chart.
Sign rulers
Mars rules Aries, Venus rules Taurus and Libra, Mercury rules Gemini and Virgo, the Moon rules Cancer, the Sun rules Leo, Pluto (traditionally Mars) rules Scorpio, Jupiter rules Sagittarius (and traditionally Pisces), Saturn rules Capricorn (and traditionally Aquarius), Uranus rules Aquarius, Neptune rules Pisces.
The chart ruler
The planet ruling your rising sign is your chart ruler. Its sign, house and aspects colour the whole chart. Leo rising is run by the Sun; Virgo rising by Mercury.
Dispositor chains
Follow each planet to the ruler of its sign, then that planet to its ruler, and so on. If the chain ends at one planet in its own sign, that is the final dispositor: the planet everything else reports to.