This is not going to be a definitive guide to the meanings of the planets, but more a what each planet means.
The planets are in astrology planets, they are not the stars! just thought id say that. Astrology works off of the planets, not the stars. Stars shine by the own light, planets do not. And for the sake of astrology, Pluto I do believe will remain a planet!
The planets in order from outer to inner are
Pluto, Neptune, Uranus, Saturn, Jupiter, Mars, Earth, Venus, Mercury and
the Sun. The Sun being at the center (its legal to say that these days
without getting burned at the stake ya know.
So here is a rough guide to the meanings of the planets.
SUN 
Its symbol is a circle with a dot
in the middle signifying eternity and the power of spirit of primal motion.
The most powerful of all the planets in its effect on a person, When people
say I'm a Pisces or whatever, what is meant is that when they were born
the Sun was in the sign of Pisces. That's all it means. It does not take
into consideration that say Venus was in Taurus or for that matter every
other planet was in Taurus, it only says that the Sun was in Pisces. Naturally
such a person would show far more Taurian Characteristics than Piscean,
though the person would still be Piscian at heart.
The sun signifies the underlying self, the Heart of the person if you like, it would say more who that person actually is, the Sun would express itself in the sign that it was in at that persons birth. This is not necessarily how that person appears but how they are.
MOON
Its symbol is two semicircles, reflections of the power of spirit, it
stands for the feminine principle of motherhood.
This planet shows the persons outward mannerisms and general behavior,
example for me my sun is in Pisces, which would give the piscean traits
i.e. quite poetic passive etc. however my Moon is in Gemini, so I tend
to waffle on endlessly as its the moon that's doing the expressing not
the sun.
MERCURY 
Its symbol contains 3 symbols the circle of spirit is over by a part reflection (the semicircle) all of which is over the cross the symbol of earthly material matters. This is the planet of communication, that's physical and mental, so it covers all your thinking, mentality etc.
VENUS 
Its symbol is that of a circle of spirit over the cross of matter, it is the symbol for them feminine. Is about your Relationships with others from marriage/partners even business partners, so where this appears in your chart shows how you relate to others.
MARS 
Its symbol is that of the circle of spirit, it used to have the cross
of matter directly above it (the same a the sign for Venus only upside
down), the cross being above (ok arrow) showing the planet is more connected
with material things.
The planet of war! OK the god of war. This planet shows where your energy
is going. Mars, everybody has a mars and naturally every planet in there
charts. Its where these planets are and how the interact with each other
that is the key. Mars then is about energy and where that energy goes.
JUPITER 
Its symbol is of a half-circle of soul above the cross of matter. Its about how you will prosper and expand, its if you like the planet of luck, so for luck look to Jupiter, with expansion its about how you grow, physically and mentally.
SATURN 
Its symbol is the semicircle of the soul with the cross of matter at the top. Its all heavy and slow! is Saturn. Heavy slow and cold, no fun at all, but can be a learning planet also. Every now and then it goes retrograde. Which means it appears to travel backwards. It doesn't but appears to. a bit like if you were in a car traveling faster that another car and you over took it. The other car from your perspective would appear to be going backwards, though it clearly is still going forwards. Some planets do this also. So sometimes when you've got over a problem it seems to go away only to come back again a little later, this can be Saturn doing its retrograde thing.
The Extra-Saturnian Planets
They are called this as well they are past the orbit of Saturn but also because they cannot be seen by the naked eye, the first ones believe it or not can be. The Extra-Saturnian planets have more effects on a generation as regards which sign they are in as they move more slowly.
URANUS 
Its symbol is said to be the H for Herschel who discovered it. Its about change any form of change, so in your birth chart its where you're going to get the most amount of changes. So for example Uranus in 4th house, the 4th house being your home would suggest you are likely to move a lot. If Uranus affected Venus would effect you have more relationships or your relationships are subject to changes.
NEPTUNE 
Its symbol is said to be the trident of Neptune by others to be two curves with the material cross between them. The Mysterious planet the arty planet. The planet was found by indirect means, sort of "well if this happens and that happens then there must be a planet there. And there was, Neptune, and that really describes the nature of Neptune. It about the non-material or you urges that way. Also connected with water (as in Neptune).
PLUTO 
Discovered in 1930 by Lowell Observatory and was first called Pluto-Lowell Hence the PL sign the P with a long lower leg being a combination of a P and an L. This is the planet that creates great changes its the "out with the old and bring in the new" planet. Sometimes when things end, its only a process of renewal, its Pluto that does this elimination, renewal and regeneration cycle. I tend to associate it with the nuclear 'stuff' in the past it was bombs which was 'Mars stuff', now its Pluto the atomic 'stuff'.
The symbol for Mars is the circle with the arrow coming up and to the right, sure you've seen it, as it symbolizes male. Pluto also has a sign similar which is the same sign but with two arrows coming out of it. Sort of a bit more powerful!
