Picking up clutter is a time consuming process that can cause a lot of stress. Start with one small area in your home and do one area at a time. Get 5 small boxes or 5 trash bags to sort thing out in. Labet each box or bag with these labels: Give Away; Sell; Store; Keep and Trash. Throw away the trash. Box up the items you want to store. Also box up the items you want to sell and the items you want to donate. Put everything else in it's proper place in the house.
Accomplishing one small area of your home can give yourself the confidence to do more. Try to make your decisions quickly and you will be less likely to hang on to something you don't need. Make sure to maintain the organization of that one clutter free space. Become protective of the areas you've organized. Refuse to let them become reinfected again with clutter.