Whatever the merit of the rule ? and both historically and logically, there's not much ? there's a substantial body of opinion against end-of-sentence prepositions; if you want to keep the crusty old-timers happy, try to avoid ending written sentences (and clauses) with prepositions, such as to, with, from, at, and in. Instead of writing "The topics we want to write on," where the preposition on ends the clause, consider "The topics on which we want to write." Prepositions should usually go before (pre-position) the words they modify.
On the other hand ? and it's a big other hand ? old-timers shouldn't always dictate your writing, and you don't deserve your writing license if you elevate this rough guideline into a superstition. Don't let it make your writing clumsy or obscure; if a sentence is more graceful with a final preposition, let it stand. For instance, "He gave the public what it longed for" is clear and idiomatic, even though it ends with a preposition; "He gave the public that for which it longed" avoids the problem but doesn't look like English. A sentence becomes unnecessarily obscure when it's filled with from whoms and with whiches.
