Cinders, the way I make my posts longer is by the following:
-read good books (inspiration weighs surprisingly heavy)
-Describe different things that you know would catch your character's attention. Know your character inside out (or at least get a good general idea. Don't be afraid to have their character sheet tab open while you write). Their looks and personalities will cause them to be attracted to different things.
-Be detailed, but don't go full out Tolkien (aka, don't describe every single detail). Add enough so that we know where you are. Add what you are wearing is good for a starter post or for when they just woke up.
-Screw stuff up. Have them spill milk on their shirt and then have them react. Don't just go "she dabbed her wet shirt with a towel". Add a thought or something else to go with it. It makes them feel a bit more alive and human. Of course, don't overuse this as it can get over the top. Just once every few posts. If you find the RP being a bit null, it's a good way to stab at the embers. Especially if it involves another character.
-Whenever I join a RP, I get a feel on how my character will be introduced into the story. I think about it. Like, hmm, he is scared of spiders. I think I'll make him dream about being chased by Shelob (a giant spider if you haven't read/watched Lord of the Rings). Then I laugh wickedly and wait for the RP to start a thread.
-You can make affiliations with other people's characters. This will probably not work in this RP, but it can in other ones.
-Know their history. I have a character who has flashbacks and I add those in occasionally. You can burn some words by talking about how they miss their ex's voice or how they are in deep thought thinking about their best friend who they'be had a crush on since fourth grade. Of course, this will work with any memory, romance related or not.
-Add a part of yourself in your character. It just makes it easier to play as them and reactions will come more natural. This helps me a ton to write several characters from different RPs. I like my food so I made Aaron go to the food.
---
I'd like to note that these help me and I'm sure that some will help you. Maybe not all, but some. Don't get discouraged if one of these points lead you down a deadend. We're different people and different things work for us. Also, I followed your post the entire time I was writing mine and used it as a guideline :)
"Success is stumbling from failure to failure with no loss of enthusiasm." --Winston Churchhill
Fall Month: 1 
Night 
Clear Moon: 
