If in doubt, take away the second person in the sentence and you will quickly see what is wrong. We don’t normally say She gave the books to I. Nor do we usually write Me went to the zoo, unless we are the Cookie Monster.

Dialects
One word of caution here. English comes in many varieties and there are countries where the dialect uses he and she instead of him and her. In the past, dialects were considered incorrect or uncouth. Nowadays, many people write in dialect and challenge the authority of Standard English. As one example, Shani Mootoo’s latest novel is entitled He Drown She in the Sea. So, if you are editing something and come across language that looks wrong, just make sure it is not there on purpose.

Which and that
Some people think it is important to know which of these words to use when. Grammar rules in the US are strict about this. Rules in Britain are much less rigid. As usual, Canada falls somewhere between the two. Here is the rule: which is used for a clause that can be removed without destroying the meaning of the sentence. For example, The rose bushes, which we planted last year, have flowered. We could take out the which we planted last year and the sentence will still have meaning. The rule says that should be used when the clause is necessary for the meaning of the whole sentence. We would say The roses that we planted last year have flowered better than the older ones. Here is another example: The meetings, which I don’t go to, are long. And The meetings that I don’t go to are long. In the first case, the speaker avoids all the meetings. In the second case, the speaker avoids only the long meetings.

Conventions
Now let us dispose quickly of a few conventions that some people still consider rules.

“NEVER END A SENTENCE WITH A PREPOSITION.”
Prepositions are words like up, on, at, in, to, from, by, for and with. Forget this rule. Almost all good writers end sentences with prepositions sometimes.

A sentence is a fine thing to put a preposition at the end of.
—William Zinsser

“NEVER START A SENTENCE WITH AND, BUT OR BECAUSE.”
Forget this rule too. These opening words, used in moderation, can make the text flow more easily. William Sabin, an editor of Gregg’s Reference Manual, recently pointed out that those who object will frequently begin their complaints with But you can’t do that!

“NEVER SPLIT YOUR INFINITIVES.”
The infinitive is the form of a verb that includes to, as in to go, to do, to split. To “split an infinitive” is to insert a word in between the to and the rest of the verb.