don't be fooled by the different rating scale, even 1200 players tend to be very solid on ICC. it's very unlikely your rating would be even close to your RHP rating, especially in the 5-minute pool. I think I went down to 800-900 when I first began playing blitz, and only recently broke 1500 for the first time. the general blitz pool is slightly easier, but still very tough.
there are GMs with 1800 ratings in the 5-minute pool. granted those aren't the blitz specialists (which are around 2500-2700 on 5-minute pool), but it tells you how tough the crowd is.
so how to improve? well, firstly, you need a lot of experience. that means you need to play a lot. preferably also analyze all your blitz games right after finishing them. especially the opening, you can't underestimate the importance of strong opening understanding in blitz. the reason is, a minute of time is probably worth close to a full piece in 5/0. if you can win time in the opening, while not getting into a bad position, you're already halfway there. time is usually the most important aspect of a blitz position. which is also why technique is important, you simply won't have time to mate with KNB in 2 minutes, you need to be able to do it in 20 seconds or it'll be a draw almost 100%.
of course tactics are important. but I think their importance in blitz is highly exaggerated. I was about as good at tactics at 900 blitz as I'm now at 1500. it never made much difference. it's much more important to know your positions like the back of your hands. which brings us back to the openings, because you won't know your middlegame positions if you haven't been in it a million times before, and you never get to them in the first place unless you know your openings.
endgames in blitz are a bit similar, and a proficient endgame player will probably be lethal in blitz, as practically all blitz endings are misplayed. you see even GMs screw up basic pawn endings every day on ICC. in time trouble, of course, but that's exactly my point.
play solid. don't weaken your position, even if it's probably a strong move. weaknesses bring complications, complications require thinking, thinking requires time, and time trouble loses games.
the basic thing is, you need to play, play, play and slowly you'll improve. playing 20 years of slow games will probably do it as well, but I think the main point is the same: you need to gain mileage to improve at speedchess.
that said, I'm a crap blitz player, so everything I said should the taken with a pinch of salt. these observations are all based on my personal experiences and different approaches I've taken towards improving at blitz in recent years, as an adult player.