If you already have a website or blog, look for vendors that offer related but noncompeting products and see if they have an affiliate program. Stick to familiar products and brands—they're easier to sell. For promotion, place simple text or graphics-based ads in appropriate places on your site; you can review or recommend products or create a dedicated sales page or website to promote a particular product.
Most of us are guilty of hanging onto things that we never use, myself included. Take a day and go through all your old stuff and get rid of some of it! One tool that is really helpful for this is Decluttr. You can enter the number on your item’s barcode [into their valuation engine] and they’ll give you an instant offer. Then you simply pack all your items into a box and ship them off for free.