I know that a lot of people like to write dramatic and emotional stories. To project this feeling onto your readers, has proven to be quite hard for a lot of people. Some people over-do it in a boring way, and others don't mention enough descriptions which makes their stories difficult to see in your mind.

DESCRIBING A PERSON

Only mention relevant details. It's my experience that you won't remember all the details after a couple of chapters, anyway. In some books the height of a character is described because the character is quite short or tall and feels insecure about that. Because this part of the character's description is so important to understand the character's actions, it is smart to mention their height. If the writer wouldn't do that, the readers wouldn't understand why a certain character never wears high heels, or does it all the time.

On the other hand, it's easy to write too much about a character. The writer can tell the reader that a character has red hair, green eyes, is kind of tall and also kind of skinny. I wouldn't recommend this for two reasons. First of all it's just too much. Second of all, it's very impersonal and saying nothing about the character's inside. If you want to mention all these details do it like this: 'She had very lively red hair that framed her face like a flame, while her green eyes were very calm and composed. They made strangers trust her. She didn't even have to try. Her tall and at the same time very skinny figure gave her a quirky look. Sports were not her thing.'

The most important thing to keep in mind is: show, don't tell.

When you write from the perspective of your main character you have to be careful to describe things as a real person would. A real person wouldn't look at the mirror in the morning to suddenly discover that she is a very hot tall girl with long black hair and the bluest eyes the world has ever seen. No one would describe himself in such a way. You have to weave small parts of description into daily conversation if it is important description, if not, you can leave it out.

DESCRIBING AN OBJECT OR A PLACE

For objects the same things count as when writing about a person: only relevant details and not too much. Only describe objects that are important for your story. Maybe a necklace your character has a special history with, or a room that sets the right mood for the chapter you're writing.

When you write from the perspective of your main character describe objects and places as your character is taking them in. When someone walks outside the first things he will probably notice are the bigger things (the sky, huge trees etc). The little details come last.

It is also important to realise that characters don't just see the world, they feel, hear, smell and taste things as well.