In a science perspective, a New Moon is when the moon is dark and is in front of the sun which blocks the sun's light from shining on the side of the moon we see. A full moon is when the sun's light shines on the entire side of the moon that we see.
From a magical perspective, a New Moon is a time when someone might be ready to start something since it's the first phrase of the moon (however some might consider it the last). The New Moon is the time to start building on to something. It's also a good time for people to start refreshing their selves and to start getting more productive in something. It's a good time to start planning something to. Anything to start something is good on this phrase. A Full Moon is generally consider when magick is at it's peak and spells might have a better of working during this time. Well... with the right moon phrase all spells that correspond to a certain phrase of the moon will have a better chance of working. Some teachers even say children get more active when it's close to a full moon. lol. It's a good time for activity and finally being successful in what you've been working on. As the waning moon approaches, it's good to start settling down. The Full Moon is also great for charging items as well because all that energy from the moon is at it's greatest. There are also more things that can be taken in consideration with this, but this is general out look.
Waxing moon to full moon: make things increase; love, money, luck and so on.
Waning moon to new moon: make things decrease or cast spells to make things go away
some traditions of magick view the moon phases as important for spell casting. others do not (hoodoo off the top of my head)
a love spell to make love increase should be performed by the waxing moon and reach its apogee on the full moon.
a love spell to break up or end things should be cast as the moon wanes
others more knowledgable than I can give you greater details, but you can look at day/hour correspondences if you wish to invoke deities associated with them
venus-aphrodite for example has a her day on Fridays. you can look up her "hour" in the correspondences which will tell you when after sunrise or sunset her "time" is. (nb. youll have to look up the sunrise/sunset time for your local area and make your calculation.) so her time is 7 days a week but her special day is Friday.
I use Aphrodite as an example since you asked about love. she is the goddess I turn to for that and who I am most familiar with.