One of the major reasons people check their horoscopes is matchmaking. After all, if personality is clearly laid out by a person's sign, then it should be pretty easy to tell whether or not that person is going to be compatible.
It's not as simple as that, of course. Other factors in a person's horoscope can influence those basic rules, or even counter them entirely. Just because a person falls within a sign does not mean they're going to be a perfect match for the general depiction of that sign. Still, it's fun and interesting to check for compatibility through a horoscope.
As a general rule, your perfect match is likely to be at the opposite side of the Zodiac from you. That is, Aries with Libra, Taurus with Scorpio, Cancer with Capricorn, Leo with Aquarius, Virgo with Pisces, Sagittarius with Gemini. Those signs opposing each other across the Zodiac tend to balance out, supporting each others strengths and countering each other's weaknesses provided, of course, that the personality differences can be smoothed over.
As an example, Cancer has a very strong family instinct.î Cancers want to have a strong and secure home life. This mindset is likely to drive away several other signs, like dominant Aries or travel-oriented Sagittarius. Capricorn, however, has a similar attitude towards home and in general, the two would get along just fine provided, of course, the Cancer could learn to cope with the Capricorn's penchant for gloom and depression.
The signs that definitely do not get along are the ones that have a core difference. Sagittarius is known for traveling, and would drive the home-focused Cancer to distraction. Detail-oriented and critical Virgo would grate on the nerves of self-centered and bossy Aries. And bright and cheerful Libra would never be able to handle a life darkened by shady, mysterious Scorpio.