Learning fly fishing from a video or a book is really hard as it does not tell you about your mistakes. I recommend finding a competent instructor. As casting a fly is something that gets automated I would also recommend to wait for the next spring to allow your muscles to forget some of the wrong motions.
I used to instruct newbies in our club and there are some common mistakes learned from casting lures.
To improve your technique you could try some of the following:

• use about 30 feet of line at first - much more is more difficult much less will lure you into moving too fast
• keep your line tight with your left hand, slack line will rob speed
• attempt to stop the backwards movement at 12 - that is plenty for most cases - 11 to 1 is for playing to entire 30 yards
• a tight line will tell you when the backwards movement is finished, learn to feel it by watching it
• waiting too long will make the line a little slower, not waiting long enough makes your line drop before your feet, better wait a little too long until you get the timing right

Generally people who cast fly badly, move the rod to much and with an excessive frequency. I didn´t meet a single one who was too slow. Most of them also allow the line to go slack between the hand and first ring