A body scrub is the fastest, cheapest and easiest cosmetic that you can make yourself: no heat is required and it uses stuff you already have.
The scrub I make the most often is a combination of sugar and oil: brown sugar, white sugar, or both; mixed with almond, olive, sesame, grapeseed, or any base oil you like. You want just enough oil to generously coat the sugar without leaving the sugar sitting in a pool of oil. The sugar should clump without any dry spots in it. The sugar and oil scrub works best on dry skin; use it in the shower before you turn the water on. If you use it while your skin is wet it will dissolve pretty quickly. If you want a scrub that you can use on wet skin, ground coffee can be substituted for sugar. This is nice in the morning because it wakes you up but doesn't make you smell like coffee afterwards. You can also try finely ground nut shells (such as almond), polenta, or just about any fine, grain-y stuff that won't dissolve. Any scrub you use while water is running will wash away as you use it so the exfoliation will be a little milder.
A great, if not entirely necessary, addition to the scrub is a little essential oil. You can use one scent or a custom blend. I like citrus oils like grapefruit or lemon in my scrubs, or lavender. Be careful with essential oils especially if you are trying a new one. They are strong and they can cause allergic reactions. Don't apply undiluted oils to your skin: always mix them with a base oil.
Whatever oils and grit you use the scrubs work the same way. Rub the scrub all over your skin, spending extra time of dry and rough areas. The oil in the scrub will make the floor slippery so be extra careful. If you are using a sugar based scrub, it will rinse off and dissolve when you turn the shower on. Coffee and other non-dissolving scrubs can be applied to wet skin (but not directly under a blast of water) and then rinsed off. If you just rinse off without soap, a thin layer of oil will be left on the skin. The scrub is good at getting you clean off of your skin, so you probably won't need soap afterwards anyway. If going without soap freaks you out, try it once on a day when you don't feel too grimy. You might be surprised how clean and soft you feel. I think the way skin feels after this scrub is way nicer than the super dry tight-skin feeling after I use soap.
Store your scrub in an airtight container. Make sure the lid is shut before you turn the shower on. The sugar will dissolve if gets water into it.