I need help understanding tarot readings.  I have my own set of cards and a copy of what each one means, but when you give a reading to someone, how do you know if you are doing it right or not?

Generally people will let you know if you are right or not during a reading.
However,before you do readings for people it is important to get to know
your cards. I usually take the following steps when I get a new deck;

1. Throw away the little book of interpretations that comes with the deck.

I do this because I feel it is important to let the cards themselves tell me
what they represent,remember ,any cards meaning can change depending
on it's position and the cards surrounding it.

2. I carry the cards with me everywhere I go and sleep with them under
my pillow for at least the first week, handling them frequently.

This helps the cards to absorb my vibration so that when the time comes to
use them in a reading it is easier to attune myself to them

3. Choose a card from the Major Arcana and meditate with it, allow your mind
to step inside the card and learn from it.

4. Trust your instincts, they are often right.

Don't change your reading to make a card mean what you think it should
mean because that's what the book says,trust what your inner self is telling
you.

Finally you will know when you are getting it right, you will look at
the cards spread out before you and they will reveal their message
with clarity, you will be able to give a flowing, precise reading without
hesitating or struggling. It's a good idea to practice on someone, a
friend maybe, to help you get over any nerves you may have and
develop fluency.

 Hope you find this helpful it works for me and I hope at least part of it
works for you good luck.

You could always join our free Learn Tarot course too

Patience. If it is a friend they are generally willing to help you and tell you where things are right or wrong. Tarot isn't something that you learn overnight. I do agree with Inner Peace...throw those litte white book (lwb) away! Well not literally but at least hide it in a drawer or something. You look at the card and let it speak to you. It helps a great deal if you have a deck that you're very connected with.

By connection I am speaking of one that you are drawn to, mostly by the artwork but it could be other things also. You want to look at the cards and feel as if you're steping into that card's world. When that happens you will be able to "hear" what the card is saying to you.

IE:

Six of Swords: Traditional Rider Waite images is: A woman is sitting forward on a boat surrounded by six swords. There is a man behind her in the boat pushing it away for you the reader. Ask yourself questions and put into context of the person you're reading for.

A) Is she leaving something or going somewhere different?
B) Is it a positive or negative thing?
C) Is you/friend/whoever leaving or are they going forward to something new?
D) Is it possible not to be in their best interest.

My only real piece of advice though is this:

Do NOT be afriad to screw up, it is through mistakes that we learn.