As most people know, Mars is the God of War and the ruler of Aries. Astrologically it signifies aggression and energy. The planetary symbol is identical to that used for the male gender. (Look at it carefully and see if you can figure that one out.) In a woman's chart, Mars' placement indicates the Sun or Ascendant sign of the men she'll find more attractive. This does not mean that she'll be compatible with men with this Sign, only that she'll be drawn to them.
The House and Sign placement of Mars will indicate an area where a lot of energy will be directed. It can especially become aggressive if negatively aspected, i.e. Squares or Oppositions. Mars transits will have a similar effect as it goes through a Sign or House.
Recall that the basic Aries philosophy of life, particularly the males, is to shoot them all and let God sort them out. They're natural warriors and have nothing but disdain for those they consider weak, whiney, cowardly or stupid. Mars does not inspire patience or benevolence and is considered malefic. Mars is often involved in aspects related to violence and accidents, especially when Pluto or Saturn are involved in its aspects. When Retrograde, the response will generally be passive aggression in the areas ruled by the resident house. Its placement or transits in the Signs/Houses will carry the following or similar influences:
1st House/Aries: This is Mars' native environment and will generate a lot of energy, ego and aggression. A person could easily be their own worst enemy with Mars on their Ascendant. They'll be perceived as aggressive by others and are often unaware of this projection themselves. On the positive side it can provide a lot of impetus and motivation for pursuing goals since they will want to be the best or first in their field. They'll always be in a hurry or doing something and will have little patience for those who are less active.
2nd House/Taurus: This placement is not particularly comfortable and will predispose the person to be a bit too tied-in with their possessions as part of their identity. They're likely to have a strong drive to "keep up with the Joneses" and want to have the biggest house, the nicest car, etc. Nonetheless, they may not maintain these overly valued possessions as much as they should.
3rd House/Gemini: The thought process will be greatly quickened, especially if aspected with Mercury, and the attitude will be noticeably aggressive. If they disagree with someone or something a calm discussion to resolve the dispute is unlikely. These folks will have a temper and tend to overreact to anything they perceive as opposition or criticism. Recreational fighting in the form of animated arguments are likely. However, they're also likely to be very successful because they'll have the strength and ambition to go the distance. These are the kind of people who wind up in high places and you'd do well to be considered their friend.
4th House/Cancer: This placement will direct a lot of Mars energy into building, improving and redecorating the home. The Mars restlessness could also be expressed by moving to another house on a fairly frequent basis, perhaps by purchasing "fixer uppers" and then selling them for a profit. On the negative side there is a possibility for abuse, perhaps in their past. If Mars is retrograde here, it could indicate an inclination to be passive aggressive with respect to one's family.
5th House/Leo: An active and rewarding love life is likely and they'll appreciate a responsive partner, if you know what I mean. Much enjoyment will be found in parenthood, but if negatively aspected, this placement could incline the person to view children as possessions and be fairly dictatorial as a parent. Pursuits and hobbies of a creative nature are likely to be rather physical or involve weaponry, e.g. martial arts or fencing and collecting guns or knives.
6th House/Virgo: Mars is aggression and Virgo is meticulous and critical. Put them together and you have someone who can really create a morale problem at work (another 6th House domain). In other Signs, the aggression will be expressed more in synch with the character of the resident sign, but definitely will throw a lot of energy toward work ambitions. Health is also a 6th House item. There could be a tendency toward skin problems in the form of rashes or allergies, particularly when the individual is stressed.
7th House/Libra: A lot of energy will be invested in relationships and there will be a lot of desire to make them work. It is likely that any relationships will involve a lot of talking and other activities that keep it from getting stale, e.g. joint hobbies or interests. If afflicted, Mars impatience can be a problem, but the determination for success can be used to overcome it.
8th House/Scorpio: This is the House of primal instincts, death and other people's money. Throw Mars aggression and energy into that environment and anything could happen. There is likely to be a very strong sex drive that requires satisfaction in order for the person to function properly in other areas. They're likely to be very intuitive, especially with regard to their partners and investing. There's a fascination with anything hidden, making this a likely aspect for detectives or even surgeons. Psychic abilities are also possible.
9th House/Sagittarius: The domains of this house include long distance travel, academia and legal matters. The Mars influence will direct a lot of enthusiasm toward these areas. Excursions abroad on minimal funds are likely, which will bring a tremendous amount of pleasure. Higher education pursuits are also likely to be satisfying, particularly when colored by the Mars love of competition. However, Mars impatience could be a hindrance and means to deal with this should be pursued, perhaps by participating in sports to dissipate any negative energy.
10th House/Capricorn: This has the potential to be a very fortuitous combination since it might lend some energy and optimism to a sign ruled by Saturn, which tends to slow down and inhibit. However, in the 10th house of community status and reputation, any aggressive tendencies need to be tempered properly or it could cause some significant reversals. Burning bridges with Mars temper tantrums and sarcasm can definitely be counter productive.
11th House/Aquarius: Mars in this locale can provide the impetus for significant group activities and perhaps even activism. Its the stuff civil disobedience and, with Uranus aspects, general social reform. Strong views that may or may not have any substantiation are likely, but leadership with lots of energy and the ability to spread that enthusiasm to others is likely.
12th House/Pisces: On the positive side, this could yield a high degree of compassion for others and the desire to help share their burdens. However, this is a somewhat contradictory placement for the God of War. Numerous dissatisfactions of a vague nature are possible and this person could easily be on a first-name basis with their psychiatrist. This has the potential to be War of the Worlds turned inward unless tempered with positive aspects to the Sun, Venus, Jupiter or possibly the Moon. Any aspect to Pluto or Saturn could make this quite a dark influence.