Meaningful posts and patience is the best tips I can give. Be active when you can but don't feel you need to be on here 24/7. When you join conversations try to add something meaningful to it. You're not expected to be a writer but something more then "Wow that's cool". Comment on the threads you're interested in.
Which leads to the last thing, if you're going for Colonial, the patience I mentioned before is key. Depending on how active you are, how meaningful your posts/threads are, how you interact with other members, it could happen in a month or it could be three months. A high post count and reputation doesn't necessarily mean you will be promoted quicker. Although except on rare occasions, it won't happen until you've at least met the 100 post mark.
There is a dedicated thread for Fallout screenshots which you will find in the Fallout section. Obviously
. Feel free to post as much as you want, but do use the spoiler function if you post lots of them.
Other then that just practice the golden rule and have fun! Welcome to GUN!!!