How to start?

I would love to start doing more dressage with my horse. I believe she's very unbalanced. She doesn't pick up her right lead as well as her left lead. When we jump, she very rarely will land on her right lead even though I set her up well and ride her to land on the right.
She's also very stiff when going in a circle to the right. She's pretty good about circling to the left, but she drops her shoulder and really drops into the circle when we go to the right. She can flex perfectly to both sides, so I don't really know what that is.
She doesn't move as well through her hind end as she should. She gets more impulsion from her front end, which makes her jumping kind of awkward and she just feels a lot more stiff than she should be.
She likes to root her head down when I slow her down, which can get very annoying :/ She drops her head pretty low (too low) at the walk, so I try to loosen my reins, but then picks it back up at the trot, so I'm constantly having to adjust my reins.

I've had her for two years and we've gotten pretty far. But I've always focused more on jumping than flatwork/dressage. Now that I look back, I'm really mad at myself for doing that because she could be so much better now.
So basically I'm asking for advice. Possibly advice on how to address all these issues, or where to get started with a horse like mine. Thank you!

I've had the same issues with my horse in the 10 months I've owned him, although we rarely jump, these are things I do to loosen him up and get him working properly.

First, if you can I would look into getting a dressage trainer to help with your riding. If you already have a trainer, ask for a break in jumping and really focus on dressage.

The absolute most important thing in dressage is how you ride. If you don't carry yourself correctly, the horse will not carry themselves correctly. If you don't already, try to use your seat, then legs, then reins for all aids. By that I mean try to control your horse with your seat first, then, if you're turning or asking her to move foreword your legs and then reins in a non direct way if possible. Contact should not be with just the reins, you need to have contact with your legs in seat for the horse to move properly. Of course, this is a very general description. Like I said, getting a trainer would be best, if not, read as much as possible about dressage. I strongly suggest this book, Amazon.com: 101 Dressage Exercises for Horse &... and these sites, for info. Http://www.artofriding.com/school.html http://www.classicaldressage.co.uk/

For my horse, I like doing lot's and lot's of trot poles, riding on hills, figure eight's, serpentines, circles etc. I also do an exercise where I ask my horse to walk freely forewords, move up to slow trot for 5 or 6 strides, then promptly halt and back up for 5 steps. When done correctly, this will cause the horse to round their back and work from their hind end more. These are just some of the things that have helped me, I'm not at all a good rider and dressage with my horse is very much a work in progress, but it has improved.

It would be very helpful to see videos of her so that people on here could critique her properly.

Thanks for the suggestions! I'll see if my dad can come tomorrow and film me riding her.