If you're planning your handfasting, and want to incorporate Wiccan or Pagan correspondences into your ceremony, then you're in luck! There are many systems of correspondences, both ancient and modern, on which you can draw. The Pagan Wheel of the Year, and many modern rituals—including handfasting itself—http://www.llewellyn.com/encyclopedia/term/are based on correspondences. The four directions, the times of day, different herbs, crystals, planets, deities, trees and flowers all form the basis of what we, as Pagans, practice.
To decide which correspondences you'd like to include in your handfasting, one idea would be to start with the time of year. We'll run through some possibilities.
Spring: this is a very a popular time for a wedding. Here, you've got the key calendar points of the Spring Equinox and Beltane. The earliest mention of Beltane is found in an Irish text, the Sanas Chormaic; this is an early medieval glossary, written about 900 AD, which mentions "lucky fires." A lot of people choose the time around Beltane as their handfasting date, because of the contemporary associations with love, romance and fertility (in the old days, it was a chancier time, when the faeries could play tricks on you).
You have many correspondences to choose from here, with the option of decorating an outdoor space with pink or white May blossom (it's said to be unlucky to bring this indoors, but only in certain parts of the UK), roses or spring flowers, such as pots of primroses, and just as our ancestors built twin bonfires to drive their cattle through, you might like to have a couple of bonfires between which your guests can (safely) run, in order to bring luck and fertility.
Summer: along with spring, many Pagans choose to hold their handfasting in the light of the sun. Roses are at their peak at this time of the year—a traditional Classical offering to Venus, one of the best known goddesses of love. You can also honor Venus in your handfasting with offerings of myrtle and wine.
You may like to venture out on Midsummer Eve and gather some of the little yellow flowers of St. John's Wort, then steep them in sunflower oil and sunlight for a week or two and use it in solar magic: you can wear it for luck in your summer handfasting (do a skin test first).
Autumn: many Pagans' favourite time of year is autumn, and the Autumn Equinox, sometimes named Mabon, is a period at which we have done many handfastings. You may wish to bake a loaf of bread for your handfasting, perhaps in the shape of a corn plait, or decorate the house with bunches of autumn leaves and berries, such as hawthorn or rowan.
We also do a lot of handfastings around Samhain; this is a numinous part of the year for many Pagans and despite its sombre associations, some people like to honour the fact that it is now regarded as the beginning of the year in contemporary Paganism—a good time to have a wedding, as it's the start of your new life together.
Winter: To modern Pagans, this is the time when the goddess gives birth to a shining son, the solar child of the Mabon. Some like to work with the Holly King and the Oak King, following the work of Robert Graves and visualising the ritual battle between these two powers. Others choose to honor the goddess at this time of year in her role as the Lady who gives birth to the sacred child. Many pagans believe that this is where the original legend of Christ's birth came from—in a cave, at Midwinter, the Child of Light is born. Light a white candle for Her, symbolising the return of the sun from the winter darkness and make an offering of honey or mead.
The second great winter festival in modern Paganism is Imbolc: buy a small bowl of snowdrops and place them on your handfasting altar. Light white candles. If you carve wood or make dolls, you can also make a representation of the Goddess Bride and place her in a small basket—this is an old Scots custom known as "Bride's Bed." In the Outer Hebrides, a representation of Bride would be made and decked with shells, primroses, snowdrops, and crystals, with a bright crystal above her heart. Then take a few minutes to ask the goddess for her guidance for your handfasting ceremony.
Some people will choose a time and date according to astrological factors, and you may wish to consult a professional astrologer for this. Organising events around the stars used to be common practice: Queen Elizabeth I consulted magician John Dee with regard to her coronation, and weddings, too, used to be subject to divination. If astrology is your thing, your main consideration planet-wise will obviously be the position of Venus, and witches/Wiccans will want to take the lunar cycle into account, too. If you want to have an astrological handfasting, you can take your own horoscope as a starting point and check the correspondences that accompany each Zodiac sign: wear a necklace of amethysts for Pisces, for instance, and check out the correspondences (colours, gems and herbs) for Jupiter, the sign's ruling planet.
Mixing and matching the correspondences belonging to each person who is getting handfasted, such as your astrological sign, is a way to deeply personalise your ceremony, and these can be earthly associations as well as celestial ones. We recently conducted a handfasting for a couple: the groom was from St. Vincent, so the handfasting cord was woven in the colours of his country's flag. Don't worry too much about getting your correspondences "right," since there are many different systems of correspondences from ancient times right up to the modern day, and none of them is definitive. It won't hurt to mix and match a little—what is truly important is that the symbolism that you use in your handfasting means something to you.