How do i keep my sneakers cleaned?? please help me!!!?

i got white addias and nikes but they're getting ruined by the jeans because when it rains the color goes on the white sneakers!! And i never understood how come i see other people with the same sneakers but theirs never gets ruined why is that?? what do i have to do?? is there any way that i can clean the ones that's aready ruined?? PLEAS HELP ME!!!