(Note for parents and teachers: most people have a good feel for grammar without needing to be taught it: the mistakes children make in their writing are usually the result of them being poor at reading (so they find it hard to remember what they have just written and can easily loose the thread of what they're trying to say), and you can easily tell when this is the case because they don't make the same mistakes when speaking. There is no point in trying to teach children grammar to cure problems which are actually caused by their reading difficulties. Even so, there are a few real issues which are worth looking at carefully.)
You and me; you and I:-Which of the following sentences sound wrong?
Me and you saw it.............You and me saw it.............You and I saw it.
It saw me and you.............It saw you and me.............It saw you and I.
Maybe they all sound fine to you, but at least one of them is wrong. Perhaps these sentences will help you decide which:-
Me saw it.............I saw it.............It saw me.............It saw I.
All of the red sentences are correct, but the orange ones are absolutely wrong. The green one is not grammatically wrong at all: it is only considered wrong in that it might sound impolite to say "me and you" rather than "you and me" (this may sound as if you've mentioned yourself first because you think yourself more important than the other person, though it is often better to mention yourself first if you're giving a longer list of people). Two of the blue sentences are also arguably grammatically correct because they are actually shortened versions of the sentences "Me and you: we saw it" and "You and me: we saw it". If you are listing a whole lot of people who did something, it makes sense to mention yourself first so that you don't have to remember to tag on "and me" or "and I" at the end of it, so you might say: "me, you, John, Mary, Alan and Jane: we all went there together", and there is nothing wrong with speeding this up by missing out the pause (the colon) and the "we" (Me, you, John, Mary, Alan and Jane all went there together). In an effort to wipe out these supposedly-wrong constructions, schools have a bee in their bonnet about always saying "and I" instead of "and me, and this results in the appalling orange sentence "It saw you and I", a sentence which is every bit as wrong as "It saw I".
It's me; It is I:-
In answer the question, "Who's there?" do you say "It's me"? There are many idiots who claim that "It's me" is incorrect and that you should say "It is I" instead. This is completely daft: the word "I" doesn't fit with "is": it has to go with "am" instead, so they should actually be saying "It am I", and then there's a new problem with it because the order's wrong: "it" can't come before "am", so they should logically end up saying "I am it". You should ignore these nutters and stick to saying "It's me" (which is short for "It's me that's here": the alternative "It's I that's here" is simply ridiculous.
Lie; lay:-If you are planning to lay on a bed, you must be a hen: laying is what they do when they pop an egg out. You are supposed to lie on a bed rather than to lay on it, although the past tense of "lie" is "lay", so it is correct to say that you lay on a bed last night (while your hens laid their eggs).
Less; fewer:-People argue about these words which have essentially the same meaning: you are supposed to say "less stuff", but "fewer things" ("fewer stuff" is clearly wrong, while "less things" is officially wrong). So, if something can be counted using numbers, you should say "fewer", but if it can't, then you should use "less". However, there is no "more or fewer" version of the phrase "more or less", so you have to say "there were more or less fifty people there" (rather than "there were more or fewer fifty people there") even though the rule says that you should say "fewer people" rather than "less people".
Might; may:-Often the words "might" and "may" can used to mean the same thing, though only when there is no granting of permission involved ("You may go now" is not the same as "You might go now"). If you are talking about a past event in which something might or may have happened, then the word "may" is only correct if you still don't know whether it happened or not, so "He may have died in the war" means that you still don't know if he did. You cannot use "may" instead of "might" in "He might have died if his friend hadn't saved him". In the present or future tense, the outcome is not known, so "may" is valid: "He may die" = "He might die".
Will; shall:-This is complicated, so you may need to think about it carefully. You should say "I will go" if you hope that you will go or if you have a duty to go, but "I shall go" if you are only predicting that you will go. It works differently with "you will go" (where this is now a prediction) and "you shall go" (which may be granting permission or pointing out a duty). "We" behaves like "I", while "he, she, they and "it" behave like "you". Note that in Scottish English the word "shall" is considered to be foreign, so "will" is used instead in all cases, and perhaps under this influence, the use of "shall" is becoming less common in England too. Of course, in normal speech both "shall" and "will" are reduced to 'll and so any distinction between the two is completely hidden in any case.
To boldly go:-"To go" is officially classified as an infinitive, but this is actually a foreign concept brought in from the study of Latin and it should not apply to English. Even so, it can still sound ugly to put a word like "boldly" between "to" and a verb, so you might try to avoid doing it if you can. However, there are many situations where the best place for the "-ly" word is between the "to" and the verb. "He tried to quickly stop it falling" is a much better sentence than the alternatives: "he tried quickly to stop it falling" (is that a quick attempt or a quick stop?), or "he tried to stop quickly it falling" (which sounds ridiculous).