Whilst I am going to describe this for the solitary practitioner, this rite can be performed by couples and is used in covens where the High Priest and Priestess perform the symbolic rite.  

Since this is one of the fertility festivals it is appropriate to perform this ritual on this wonderful day. The version here is the symbolic rather than the sexual enactment of the joining of the God and Goddess. For this is required uniting the athame (masculine phallic symbol) with the chalice (Goddess/womb symbolism). This is usually filled with red wine to represent the blood of life though you can use juice or water.

Prepare yourself and your sacred space as you would for ritual work. Cast your circles and call the quarters. Now you are ready to perform the Great Rite.

Offer up the chalice with both hands  towards the left side of the altar. Ask the Maiden Goddess of Ostara to bless this symbol of her womb. Visualize the energy of the Goddess infusing the chalice and its contents. When you feel this is done, replace the chalice on the altar.

Now pick up your athame with both hands and offer it towards the right side of the altar. Ask the young God of Ostara to bless the athame as a symbol of his creative energies and visualize his energy filling the blade.

Transfer the athame to your right hand and pick up your chalice. Holding them in front of you, offer your blessing for the sacred union and marriage. This is my version but make your own to suit as you wish.

Maiden Goddess

Womb of life

Young Lord reborn

Fertile with life

Lord and Lady

Your union be blessed,

Sacred marriage, sacred sex.

Unite again to create life a new

To all the earth

So Blessed Be

Lower the blade into the chalice, knowing that this represents the union of the God and Goddess, the divine halves in union once more to create life anew. Feel the life flowing through the united symbols in your hands. Know that you are connected to the divine and you are part of them as they are you and all life.

Place the united chalice and athame on your alter and do not break their connection until the end of your rituals.

Some people leave them united until the autumnal equinox but personally, I have other uses during the year and the wine/juice tends to mark and sometimes corrode the metal.

When you have finished your Ostara rituals that you want to do, thank the guardians/elements you called letting them know that your rite is done, close the circle and go and eat.