First, purify your person. Take a shower, or better yet, soak for a while in hot water containing sea salt, bath salts, or Epsom salts. Allow the salt and water to neutralize any negativity within yourself; think of this as you soak. Let any contamination be washed away with the water spiraling down the drain, out of your house and out of your life. Drink lots of water to wash out your insides. Wash your hair, brush your teeth, put on clean clothes. You may also wish to drink mint tea or another tea that you find refreshing.
Second, purify your dwelling. Dust, sweep, vacuum, tidy up, polish. Air out the rooms. Wash the windows with a mild solution of vinegar and water. This allows purifying sunlight and moonlight to illuminate the room as well as making the glass more reflective to deflect unwanted energies.
Circulate through the rooms where you live with sage or other purifying incense, making sure to fumigate everywhere -- stairways, closets, underneath stairways, basement, attic, garage if attached. If your dwelling is one that you can circumnavigate, you may wish to walk all around the outside of the building wafting this smoke.
Then mix salt and water and sprinkle it around the house. As with the incense, do this around the outside of the home, too, if you can. Be sure to cense and sprinkle all openings to the outside -- doors and windows, of course, but also skylights, electrical outlets, heating vents, chimneys, ventilator hoods, toilets, and sink, tub and shower drains. Also do this to mirrors.
While you're doing these things, speak the words, "With Earth and Water I purify this space," and "with Fire and Air I consecrate this space," because that's exactly what you're doing.
Third, ward your space. If you're the witchy sort, trace a protective pentacle with the salt water on all doors, windows and mirrors. Rosemary grows in abundance where I live, so I like to use a sprig of it to sprinkle the salt water. Then I like to leave rosemary sprigs on all the window sills.
When you've done all these things, take a step back, be very quiet, look around, listen and note how different your space feels to you now.
You may also wish to perform these acts at other places where you spend a lot of time, such as work, if you can.
One last thing you may want to do, although it's not as easy and practical as the rest. You may wish to hang little mirrors in the windows or on the outside of the building to reflect away negativity. The mirrors aren't really necessary; they're just extra insurance, if you will. You should be fine just doing the other things I've recommended.
Now envision yourself within a bubble. Project this bubble around you and around your home. Nothing can pass through the membrane that has not been invited by you. Anything unwelcome bounces off the bubble. Build a strong image of this bubble in your mind. If you have a small object, maybe a clear quartz crystal or a piece of rosemary, that reminds you of this visualization, carry it in your pocket or keep it someplace handy. You can't be expected to hold this image in your consciousness all the time. But if you have this object, then at times when the image has faded and you feel you need to reinforce your working, take it out and look at it and touch it to reawaken your sense of your protective bubble.
As with all magic spells, you needn't stick with the formula offered here. If other ingredients call to you or other actions spring from you, trust your intuition and go with them.
These are my recommendations. For another approach, here's a Lemon UncrossingSpell (to break a curse). I have never tried this so I can offer no assurance of its efficacy.
 For a super-duper heavy cleansing of a home, say if you're just moving in after someone else has been living there, and if you have the time, get some dragon's blood incense and burn it on a piece of charcoal in a container left in the bathtub or shower. As soon as you light it, leave and let it fumigate the entire house. You don't want to breathe much of this stuff. Then return a few hours later and open all the windows to let out the dragon's blood fumes.
 Some additional things you can do to cleanse a new or dirty home: Walk throughout the rooms with noisemakers, rattles, a drum to frighten off unwanted spirits. Do this before censing and sprinkling. After censing and sprinkling, ring a little bell at the windows and mirrors.