Astrology is the art of using the operations of the stars. To all you scientific minds out there, yes, by "stars" I'm including plenty of things we don't call stars anymore. Asteroids, planets, comets, eclipses, space stations, space shuttles, natural and artificial satellites…
The modern applications of astrology are mostly beyond the average person, since it's not helps to get a satellite put into orbit. Here we'll cover a few traditional methods of working with the heavenly bodies.
One of the simplest forms of magic that a beginner can pick up is working with the sun or the moon. They're very obvious, have plenty of impact on our day-to-day lives, and most of all, are really, really bright. Everything else is more distant, but when the light is in your face, it's easier to manage. Some people struggle with still images, so the sun and the moon work best.
With the sun, it's important to carve out space in each of the seasons, and for each section of the day, for specific effects. This can vary from person to person, but in general: spring/dawn for things that are beginning or growing, summer/noon for things that are at their peak, fall/dusk for things that are shrinking or fading, and winter/midnight for things that are ending of dying. Keep in mind, whichever time you pick will intensify that type of situation; if you want to stop something ending, I recommend summer/noon to extend the time available, and if you want something to stop fading, I recommend winter/midnight to put it into stasis.
The moon is similar, but different. Each phase of the moon will allows you to influence reality, but it's more continuous than the sun, which is discrete. Make sure not to work against the direction of the moon's phases; if you want something to increase in power, start with the new moon for best effect.