What is the best way to deal with students in school who do not pray, and women who are immodestly dressed, yet appear clothed, and who mock advice?

Man's being affected by those he lives with necessitates guarding against associating with the corrupt, while being keen on inviting them [to righteousness] and guiding them, and being patient in that. And indeed, abandoning prayer, looking at non-mahram (definition) women, and ostentatious display (tabarruj) are major sins that must be avoided, repented from, and one must be keen on strengthening faith, reforming hearts, perfecting prayer, strengthening one's connection with Allah Almighty, and frequently remembering Allah the Exalted.