Can't Improve Rating

I've been playing on this site for about a year and have gotten WAY better in that time. But I still seem to be stuck at about the 1250 to 1300 rating. I don't seem to really move up much over time. How can I move up?

I think it's really tough to improve beyond a certain level just playing blitz. You need a lot of discipline to force yourself to analyze every game you play and learn from your errors.  It's so much easier to just keep playing, and in effect, perfect your mistakes.  Not saying you can't get good playing just blitz, just that it's a more difficult road.  Heisman is big on keeping the three components of getting better at chess in balance: play, review, and study.  Most seem to feel that playing more long time control games gives them a better shot at keeping it all in balance.  As long as you are learning something from each of your games though, you can probably do it with blitz.  Good luck!

In one year my game improved tremendously by playing 3 day/move games. 

Really, unless you invest the time and effort to LEARN about chess, your progress will always be limited.

If you're stuck on playing blitz, the easiest way to see some improvement in your game is to review your games. Learn from your mistakes and successes.

BTW - If you rating is not improving, you, in fact, are NOT improving.

You are experiencing the downside of being an instant gratification junkie.

This post is old, but I relate to it. For one year, my rating in blitz went between 900 and 1100, then it went from 1100 to 1300 for four months, and I've been stuck between 1300 and 1400 for 3 months. The progress is sluggish and I want to progress faster, but chess is more of an instinctual game to me.  So it's hard to know what's wrong with my playing style and it feels more mood-dependent than anything else.

There is nothing instinctual about chess. You have to actually study it to continue progressing.