Visit a thrift store and find jeans that are cheap jeans. In this case, the brand and the wash will not matter at all.
Make sure the jeans fits you well. The entire fashion of coloured denim is all about fitting. You do not want to wear loosely fitted colored jeans. Also, the jeans can get loose when you dye it so it is always better to get your hands on tight or skinny jeans.
Make sure the stitching of the jeans matches the color you want to dye it in.
Select a color dye for denim that would suit well to your taste. You need to learn a bit about dying and how to mix colors. In most cases, you will find an instruction manual in the dye box.
You will also need a big size tub, washing bleach, tongs, and a measuring cup. Gather all these utilities before you start out.
Fill up a large bucket with hot water and add bleach to it. This will get the denim rid of its color.
When the jeans is completely white or yellowish, take it out and wash it with a detergent.
Mix the dye in a separate tub and get your jeans ready for dying.
Put the jeans in the tub containing the dye and stir it. By stirring the jeans, you will allow it to absorb the dye as much as possible. Stir it for at least five minutes.
Now, wash the dye with plain water. Make sure you do not use a detergent at this stage. Rinse the jeans until the water runs clear through it.