Depending on the type of oil, (Petroleum versus vegetable) some are easier than others. If you have already washed and dried the clothing, and the stain is still there, you have pretty much cooked the stain in and it isn't going to come out. If you have not already washed or dried the clothing, then pre-treat the spot with a mixture of liquid laundry detergent and vinegar and let sit for about 15 minutes and then wash. Examine the clothing before you put it in the dryer and DON'T dry it if the stain is still there, you may have to pretreat and wash a second time. Drying locks the stain in place.
With the Paint, once it has dried on the clothing, depending on the material, thickness and composition, it will not come out at all, no matter what you do. That is especially true of oil paints. You have effectively painted the individual strands of fabric. If it is on something like a sweater, you might try one of those "sweater shavers" and remove the top layer or, If you are lucky, all of the paint.
If it is latex paint, you might try gently scraping with a very sharp knife softly with the grain of the material, do this very slowly, and make sure you don't snag the material. Good Luck