"Le secret d'ennuyer est celui de tout dire."
(The secret of being a bore is to tell everything)
There are two rules.
"Show, don't tell. No one wants to be spoon-fed information, they want to find it out themselves."
"Tell, don't show. You are a story-teller."
It happens that most beginning writers shamelessly abuse their ability to tell. I can't tell you how many times I've read something like this:
"Joe has always been a daredevil, but when he was sixteen he jumped off a barn roof playing Superman and broke his leg. Ever since he has had a fear of heights. The cliff part of the trail was hard for him, but he got through it."
Bo-ring. Because the writer told us everything.
"Joe hesitated as they reached the part where the trail skirted the cliff. Scott looked back and saw that Joe's face was white and drawn. He'd never seen Joe look so sick.
'What's wrong?' Scott asked.
'Is there another way around?' Joe asked. 'I hate heights.'
Scott looked down at the cliff dropping away beneath them.
'No,' he said. 'There isn't.'
Joe edged out onto the trail, one hand gripping the railing, staying as far from the edge as he could. Scott walked slowly in front of him, trying not to leave him behind.
'Sorry,' Scott said.
'It's OK,' Joe said. 'I need to get over it anyway.'
Slowly they moved across the cliff and back into the forest."
In this example, instead of saying, "Oh, Joe is afraid of heights," the writer showed that Joe becomes very uncomfortable around heights. And we understand, because Joe is gripping the rail and keeping away from the edge and we can feel his fear.
You can tell a little bit. You can tell us that Scott had never seen Joe look so sick. You can tell us that he was trying not to leave Joe behind, that's why he was walking slowly.
Just don't tell everything. Don't even show everything. Leave a little bit of mystery. Readers aren't stupid.