you
In the Romance languages, "you" is an extremely tricky word. That there exist multiple ways to say "you" in all three languages is only one problem. We're going to make it simple by sticking with a form that is appropriate for formal and semiformal associations.
There is no good memory device to link the words for "you" because they are not related to each other. However, knowing about the words and where they came from may help. First I'm going to give you our words. After that, I'll offer a little history that you can read or skip as you desire. If knowing how things work helps you remember, read it. If not, be sure to pay attention to subsequent phrases with the word "you" in them so that it sinks in.
you:
Spanish Usted (oo-stayth - th as in the)
Italian Lei (lay)
French vous (voo)
Here's the inside scoop:
Spanish Usted is said to be a contraction of Vuestra Merced - "Your Grace". It is not a pronoun so much as an honorific. When you are speaking formal Spanish, you don't say, "How are you?" but "How is his/her Lordship?" This may seem a bit too formal, but it's not: Because "Usted" gets so much use, it has lost whatever lofty pretenses it may have had. It's just a way of being respectful to someone you aren't on intimate terms with. The most important thing, then, is to know the word "Usted", and to recognize that you use the he/she form of the verb with it.
Italian Lei is just about like the Spanish "Usted". In the Romance languages, it's not just adjectives that agree with nouns. The pronouns that replace them also agree. So if you're talking about notte (night) which is feminine, you don't say "it," you say lei (she). The word for "highness" is altezza, which is also feminine. So, to keep it short, you say "She" (capital "s"), i.e. Lei. Tricky, I know. But if you start by thinking, "Her Highness" and shorten it to "Her," you'll have a story that is so annoyingly complicated that it will stick in your craw until you remember Lei on your own.
French vous actually does mean "you". But it's plural, i.e. "you guys." This one is easier to understand. Just imagine the king saying "We are not amused," and imagine responding, "I'll bet you guys aren't!" Conveniently, vous rhymes with you.
Wow! That's a lot of nonsense for three little words. But the more you know, the more you can learn - more to associate things with. And in addition to learning these three words, you've learned a few things that will come in handy in understanding the grammar to come.