Having some trouble getting enough into your character's application? Here are some things that you could do to make it better!

Appearance
Well, hopefully you aren't having too much trouble with this section. It's basically a list, after all. It's more for a quick-reference for others than getting insanely detailed, so don't stress out too much, now. Just include a description of what you want people to 'see' when they look at your character.

Personality

Basically, this is where you get to describe what your character acts like. Don't just start listing things off like "Therolin is smart. He is nice. He likes clouds." The more detail you give, the easier it will be for others to get a basic understanding of your character when in play. Also, the more detail you give, the more uniquely you can define your character from the rest of the world. Just sit back and think about who your character is, how s/he would react when put into some situations. Remember to put some detail in! Consider some of the following questions to answer about personality (but don't feel restricted to them!).

What is your character like alone? Around others?
Is s/he shy? Uptight? Outgoing? Cautious? Mischievious?
Under what circumstances does you character act in what mood?
What is your character's deepest desire?
Does s/he like pups/cubs? Wants to be a parent? Have a mate?
What is your character's greatest love? Fear? Hope?
How does you character view him/herself?
What does s/he think of family? Friends? Strangers?
Is s/he he a fighter? A lover? The silent in the corner type?
What does s/he think of fighting? What would s/he do if forced into one?

History

Ah, History. This is probably the one of the most free-form parts of an application. Before you begin, you might want to jot down a few things about your character's past, just to keep them better in your mind. Depending on your character's age and activity level, you may have a lot, or not too much, to talk about. However, the minimum is three decent paragraphs, so you will have to try to make that no matter what the past. Obviously, you are not limited to anything I suggest. There is no way to cover all the possible questions about someone's past. You could have a lot of fun putting in things that happened in your character's past, so long as they are realistic.

What kind of area was your character born in?
What was his/her family like?
What kind of things did s/he do when s/he was young?
Were there any major life-changing events in his/her past? What happened and what did it do to his/her life?
Did s/he ever do anything regretable?
Did anything happen to his/her family?
What made him/her leave home?
Was there anyone special in your character's past?
Did your character change in attitude from his/her younger years to now? If so, how and why?

RP Sample
History not your cup of tea so you decided to do an RP Sample instead? If you've played this character before and have a post long enough for the 450 word requirement, you may feel free to copy/paste that post to here. Please, however, reference where this post was originally at! If you have no such post and you are working from scratch on this, then I suggest making a mock-situation for your character to be in so you can demonstrate how you would play your character. It doesn't matter what you choose to do so long as you think it displays your writing and/or your character well. You can be as bland as going through everyday events, or put your character into one big pickle, or even use this section as a practice platform for a possible version of an introductory post for your character being on the site. Quite free-form, this bit can be.

I hope these suggestions can get your mind working to fill in some more detail in your application. You don't have to answer every question that is here, nor do you have to stick only to the ones that are here. These are just here to, hopefully, give you some ideas of things you could use in your application. For other ideas, you could always skim through the accepted character descriptions.

Bonus Tip: If the required length for you character is too much for you, you can always ask for help or even decrease the age of your character. Younger ages require less writing, after all...