Main Character?

I wanna write a fanfic to hone my very poor skills as a writer. Yep, that's pretty much it. Oh yeah, the question...

When you have a main character, do you tend to describe the character, or do you tend to not describe him/her and let the mind create an image? And why?
Also, which one do you think is better?

I say it's better not to describe the main character right off the bat. Maybe describe something that people would notice when they meet him or her like weird clothing choices or maybe your character has a scar on his face. Readers will create their own vision of the character without your input, so there's little need to provide a full out description.

While I did describe my main character quite a bit when I first introduced her (didn't really know better), I haven't mentioned much about her appearance since.

Personally, what I do is skip on the physical description unless it's important to the character. For example, I don't describe one of my character's physical looks because it has no bearing on who she is and what she does. On the other hand, I do describe another character's physical traits because they're an important part of how he sees his world, the people around him, what he thinks of them, and what he thinks they think of him.

What I do describe is the character's feelings, no matter what. To me, that's what's important to the story. How the character feels and thinks, so you should show that. It makes them more real.

So yeah. I personally don't find physical description that important to describe unless it affects them as a person.

(This is really confusing, so ask for clarification if need be.)

Don't dump a ton of information about your character at any one time, it's a horrible thing to do and it pulls the reader out of the story very quickly. Slowly reveal details of the character's appearance over a period of time that is dependent on whether you're writing in third or first person (I don't write in second person, so I can't help with that).

In first person details like that are naturally going to be revealed more slowly, unless the character has a habit of looking at their reflection often (which is a valid thing to do for a vain character). The details are only going to be revealed when the character notices a change in themselves or notices the reaction of another to their appearance (e.g. The man recoiled visibly when my hat was removed, the myriad of scars crisscrossing my face have a habit of doing so to those faint of heart.).

In third person you can reveal them a tad more often as in third person it is a character watching the scene from an external viewpoint and the appearances of characters can be noted without interrupting the flow too badly (e.g. James removed his dark grey cloak and revealed that he had been wearing a rusted chain mail shirt the entire time, despite his claims of not having any gear of his own. The shirt had obviously been of a high quality at one point in time, a fact that made the others in his group reconsider the well-muscled 'street tough' who had been traveling with them thus far. Though his hands were calloused like those of a warrior, they were clean, meaning his story about living on the street was definitely concocted. When one of his companions made as if to speak James glared at them with his piercing grey eyes, ending any possible discussion on the matter.) If you notice, throughout the example information is given slowly, while the story continues around it. A bad example is one where all the information is given at one time and nothing happens at that time. (e.g. James was a tall man with grey piercing eyes, and beneath his dark grey cloak he was wearing a rusted mail shirt that had been fine at one point.

This is also a case of 'show but don't tell'. It is always much better to show a character's trait rather than telling us it. "He towered over those in his group." is much better than "He was tall." in anything.