When we say "declare Sacred Space" we are saying the same thing as "cast your circle", because that is what you are doing.  When you create your magical circle you are actually creating a "Sacred bubble" within which you will do your ritual work. 

Each tradition has its own style or way of going about this, so the "proper" procedure will depend on the tradition you follow or what you feel is right for you.  If you are new at this, I suggest you try the a few variants and see which is most comfortable for you. 

There are a few key points to remember when making your determinations:

First and foremost, you are preparing a space for welcoming deity.  This will be a sacred, holy place.
·    You will be inviting the four elements and directions which compose all things on this planet.  These elements will assist your deity and you in accomplishing your goal.
·    When casting your circle, move in a clockwise direction.  To take your circle down move in a counter-clockwise direction.
·    Do not go into a ritual while you are angry or hurt.  This could turn very ugly if you do not have your emotions under control.
·    Gather and prepare everything you will need before you begin - this way you won't have to keep cutting a "doorway" in your circle.

The following is a brief summary of the way I declare Sacred Space.  Keep in mind that I have chosen to combine the Native American practice with Wicca:
    As often as I possibly can I like to take a hot bath before entering into ritual work.  This not only relaxes me, but allows me to sweat (a cleansing process beginning from within).  The bath can be such a wonderful experience when done by candle light, incense smoldering and soothing music playing.  This has the potential  to be a daily healing ritual for yourself - if you would allow yourself to have that. ( I know we're all busy, there are other people who want the bathroom, etc.)  but surely you can find the time to pamper yourself at least twice a week.
    Depending on the nature of the ritual, I will use the appropriate bath salts and soap.
    During my bath I try to clear  my mind and begin focusing on my ritual goal.  This is important because it helps prevent the scattering of my mental and emotional energies (a natural tendency with my Gemini Moon).
    When I am done bathing I anoint myself with the appropriate oil.
    The next thing to do is to gather the things I will need to take into circle with me and put them on my altar.  I will then light a bundle of sage and smudge myself, the altar and its contents, then the entire room.  All the while I am focusing on eliminating any residual negative vibrations or energies that might be lingering.
    The next steps depend on the tradition you follow - but this is what I do.  I light the candles that represent the God and Goddess and the appropriate incense.  Next I begin casting my circle in the East ( the direction of the new born day and the element of Water) by lighting a blue candle.  Moving in a clockwise direction I complete the circle - a red candle for the South, element of Fire; a yellow candle for West and the element of Air, and a green candle for North, the element of Earth.
    When my circle is cast I invite the God and Goddess as well as any of my ancestors who wish to attend.
    After I have completed my ritual I take the circle down by beginning in the West ( the direction of the end of the new day) and work in a counter-clockwise direction.  I generally leave all the candles burning except the God and Goddess ones to burn out.  That's why I like to use small votive candles

 As long as you remember the key points you will be able to do a fine job preparing your "temple".  Remember to relax and allow yourself to feel love as well as loved during your communion with the Lord and Lady.