This is a bare-bones, generic spell.

Use when the energies in your home or in a particular room start feeling "off" or negative.  This spell can be tweaked to suit your particular method of working or use as is.

You will Need:

Small cauldron or other fire-proof bowl for burning herbs - one that you are able to carry.
Your favorite protection oil (my recipe follows)
Clearing herbs such as sage, cedar, rosemary, etc.
Charcoal tablet (a half tablet would suffice)
Matches..
This spell uses the pentagram and the 5 elements.

Notice I Say "From" the North, South, East & West.
This is to align yourself with the Elements - you are one with them as you state your call. Trace the pentagram starting from the top point - in this spell you are invoking 'Spirit'.

Meditate before you begin - make sure you're in the right state of mind to proceed. An Alpha state is the best.

The Spell:

Light charcoal in bowl/cauldron and when burning, drop a pinch or two of your clearing herbs into the cauldron. Take a minute to take in the energy of the herbs.

Carry the vessel around the room - paying special attention to corners, closets, and places negative energy seems to linger. Project a clear, clean, white light with your mind and

Say:
"By my will I banish all darkness and let in the light."

(repeat around the room) When you've thoroughly cleansed the room, return to the center and put down your cauldron.

Take up the oil and go to the North. Trace a pentagram on the wall (window sill, door frame, etc.)

Say:
"From the North I call to Thee.
Blessings of the Spirit Be upon this place."

Go to the East 

Say:

"From the East I call to Thee.
Blessings of the Spirit Be upon this place."

Continue to the South and West, changing the blessing accordingly.

When complete, return to the center of the room and place more herbs on the charcoal.

Stand still a bit and feel the energy of the room/space.
Again, project White Light outward, mentally filling all the nooks and crannies.  When the energy feels right to you,

Say:

"This room is sealed Protected from harm.
Light replaces darkness
As I will"

So mote it be.

Note: This spell can obviously be expanded for an entire house. Just begin in the center of the house instead of the center of the room. If you are uncomfortable calling on "Spirit" for protection, you can substitute the name of your Deity.