Just as you are more than the sum of your parts, there's more to your character than just his stats on the roster. Give your character a personality; plague him with flaws (no one, after all, is perfect); and give him a history. Then, use all those things as a guidebook on how your character operates. Was his family slaughtered by Orion pirates? Chances are he wouldn't get along very well with that Orion bartender. Say his Vulcan science professor flunked him, and he ended up graduating a year after his friends. How would he behave with a Vulcan department head? Would he be resentful, or would he over compensate to prove he deserves to be a science officer? These are the types of things to bring into play so your characters come to life.

Don't just sit around and wait for someone to give you orders. Find interesting ways to keep your character busy and on display. After all, captains promote those they can see. Very often, a sim or plot thread is not going to keep everyone busy. You are going to have idle time. Use that time creatively. Playing a med character? Create a sick NE who needs treatment and roleplay it. Are you a security officer? How about having a couple of NEs get into a fist fight? Or just go to the holodeck and have a little fun. It's up to you. Just do it.

You have an imagination. Exercise it. Find interesting ways to address sim points. Make your character unique and memorable. Give old ideas a new twist. STF is only limited by how much you put into it.

This applies to both the quality and quantity of your posting. Try to establish a posting routine and stick with it. Maintain a level of quality. We all have off days, but it's important you don't write novel-length posts for a week, then suddenly drop to one-liners, only to return to novels after a few days.