Let's 1st understand what these planets represent on their own?

Mars - Mars represents our will power, courage, ability to take actions, aggressive nature, anger, our fighting ability, brother, male friends, a boy friend for a girl, a soldier, an athlete and real estate etc.

Venus - Venus is Beauty, Desire and Love, Liquid Money. Venus is the main significator of marriage. Venus represents girlfriend or wife for a man. Venus is the significator of all relations, may it be husband-wife or mother-daughter. Philosophically speaking, Venus is also the cause of all the sufferings in our life. How? Because Venus represents our desires and we get pain and suffering in our life only when our desires are not fulfilled.

House Ruler - Besides these karaka things, Mars & Venus will also rule some houses in your chart and will represent things related to that house. Of course we can't cover conjunctions Ascendant and house wise else it will never be over. So, you have to include those things at the time of interpreting this conjunction. Also, we need to keep in mind all Yogas and Raj-Yogas which their conjunction would be making to completely understand the conjunction. Here, we can only cover meaning as per karakas. 

Meaning of Mars-Venus Conjunction - As much as it is publicized as a conjunction which can make a really passionate love, the truth is that it is one of THE MOST trickiest conjunction to have. It is only one small portion of interpretation which says that a passionate lover is seen from this conjunction and this is true. But this is not the only truth about this conjunction. Mars & Venus are neutral to each other. Mars is Passion and Venus is Love. So, their combination will certainly make a Passionate Lover, but to get that result, both Mars & Venus should be in best of dignity. Both should be in friendly/exalted signs and none should be retrograde. Even if one of the two planets is in enemy sign or debilitated or retrograde and falls in Dushthana Houses then this dream conjunction can turn into a nightmare. It is because then lower traits of Mars, like anger, aggression or violence, and Venus, like Sex or Luxurious Living, will be on the fore. Then it will show someone who is or in a Physically Abusive relation. Then it can even create a Sex Addict or someone who sexually abuses others. Mars represents Capturing and Venus is Love, so Letting Go is not their trait. They will resist long and hard to get their love even at the cost of happiness of their own love. It shows a very possessive person and can easily lead to violence in love stories. They are also very much obsessed for living a rich and luxurious life. But when both are in good dignity then it shows someone who is loyal, committed and passionate lover. In that case, person will also work hard on his creative pursuits or achieving his desired luxurious life. Only key is that both planets should be well placed without any affliction. 

Who will win the Conjunction? - Mars will, at any given day. Venus is too gentle to impact Mars in any way. . 

Dignity & Strength - 

This conjunction will work well in Capricorn as Mars is exalted and Venus is in friendly sign. Likewise, they will do good in Pisces as Venus gets exalted and Mars is in friendly sign there. 

This conjunction can be really troublesome in Cancer, where Mars is debilitated & Venus is in enemy sign, and in Virgo, where Venus is debilitated and Mars is in enemy sign. 

In Aries, Leo, Scorpio & Sagittarius, Mars will have upper hand and Venus will feel lost. That means person's relations may suffer in these signs due to aggression. 

In Taurus, Gemini, Libra and Aquarius, Venus will be in friendly sign and Mars will be in neutral/enemy signs. Again, Mars's actions can be wayward to hurt the Venus. 

One or both of them turning retrograde can also turn this conjunction in to troublesome for relationship.