One of the most helpful things a reader can learn is to have the humility to accept being wrong. In my own opinion, (not to offend anyone because it's just my own opinion and they're entitled to theirs) to think we're always accurate or else the person is in denial is like thinking if a certain guy doesn't fall for you it means he must be gay. We're just NOT always going to be right with our readings. We're not even supposed to be, in my belief. Gaining the humility and willingness to admit to ourselves that sometimes we're the bug, but sometimes we're the windshield, without offense or having our self-image crushed, is absolutely the most valuable lesson we can learn. It frees us to hear the message the cards have for us, to keep the sitter in mind so that it's about the sitter and not about us and to go on to improve our skills without freezing like a deer in the headlights with self-consciousness and fear or becoming adversarial.
For one thing, it takes away our fear of reading for others because we know we're gonna hit some and miss some and that that's normal and doesn't mean we're not "good" enough. It's just how things are. So then we can go on ahead and practice on others and improve our skills without ego getting in the way. Nobody is ever 100% accurate or, even if they are, they aren't always going to know that and aren't even entitled to know that. If we read for someone and they say "no, that's not it", instead of taking it personally or thinking they're just not telling the truth, you'll be able to just give the reading, know you've done your best to deliver the message as you got it, and that at any rate, it's out of your hands what the sitter does with it. Your job is to read the cards as best you can, then let the other person and his or her Higher Power if they have one take it from there.
Once you understand all that, it takes the pressure off so you know you don't always have to be right and it's much easier to read for other people without being afraid you'll look stupid or be wrong.
Then practice will become lots of fun instead of so frightening.