You found it!! Thrift store gold that incredible vintage dress you always have wanted and for a steal. Unfortunately it smells a bit and has some weird film on it you noticed once you got in the car and admired it properly! Well don't worry almost any fabric item with care and perseverance can be brought back to its wearable glory. The first step is a gentle wash bath.
Generously fill either a large sink or a bathtub with lukewarm water. The item must be able to be completely submerged. and ONLY ONE ITEM AT A TIME! You don't want any accidental color bleeds. Always start your by using the most gentle of products i.e. Woolite, Dreft, Dawn dish soap(works great to spot treat oil and grease stains) or even baking soda. You can work up to harsher products as you feel the item needs more severe treatment. Dissolve one of these products in a pot of hot water then add the completely dissolved solution to the bathtub.
Lay the garment in the tub and pat it flat with your hands letting the solution run through the garment as it floats in the water. NEVER AGITATE THE GARMENT. Let it soak for about 15 to 30 minutes. Let water out of the tub leaving the soapy garment in the tub. Whatever the fibre, any wet garment will be much heavier, but wool will be much weaker wet than when dry, so handle it carefully when you lift it.
The secret is a good rinsing. Use the shower head attachment if your bath has one and spray rinse the garment moving the fabric folds gently if needed. Do make sure you do this stage thoroughly as you do not want to leave any residue in the garment. If the water running out of the rinse is discolored repeat the wash. I have on occasion had to wash an item multiple times.
If the garment is wool use a plastic tray to slip under the sweater and support the now very heavy weight of it without causing it to stretch. If it's cotton or linen move it into your clean bowl and let residual water drain away. Wrap it carefully in a big bath towel and get rid of that excess water. Use another bath towel if it helps get rid of more water.
Once you have gotten most of the water blotted out of the garment use weight strong plastic hanger and let it drip dry over the bath. Be careful not to use a fancy padded hanger or a wooden hanger at this stage, which might transfer wood or dye stains to the item. If the garment is unusually heavy, use a drying rack.
Okay so you washed it and it still smells a bit, usually the smell is either nicotine or mildew. Don't worry both issues can be tackled with white distilled vinegar. With Cotton or linen fabrics I will just soak in a vinegar and water solution. Other fabrics I spray the vinegar and water mixture 50/50 on with a spray bottle and let hang in the sun. This trick also works on handbags and suitcases. If you get a handbag or suitcase that has a strong odor inside, baking soda usually will do the trick. I coat the inside with baking soda and leave over night, after it has sat, vacuum out the baking soda.