We should dip the new jeans into strong saline water at first. After a whole day, then you can wash the jean. You should pay attention to wash it by hand. To wash it by washing machine would ruffle up the jean. In general, it can mitigate the faded degree if you wash and dry the inside instead of the outer. There is some bleach more or less in the ordinary washing power, in order to reflect its white effect. So we had better not use the washing power, and use the dish soap instead. There is not bleacher in the dish soap, so it will not fade jean after you use it to wash jean. The dish soap can remove grease spots, as well as cleaning.
The jean and other dyeing new clothes all contain a layer of glue. That is the source of the smell from new cloth. Except for the saline water, the vinegar can prevent jean fade too. Similarly to soak the jean in the saline water, we can put some vinegar in the water because vinegar has the effect of fixation. To the jean that are not too dirty, we had better not using washing power.