How do you train walk to canter, and help with canter leads?

Ok so I would like to teach my mare walk to canter as I have had a few in my hack and rider class workouts. I just don't know the aids to achieve this. A bit of help please. And Tess picks up the correct canter leads going right but going left, she just can't do it. And I have a bit of trouble recognising what lead she is actually on when I am riding her. So a little bit of help with this please? I do all the right things to get her on the right lead but she just doesnt do it.
Any help will be greatly appreciated thanx :P

To strike off on the correct lead:

Trot into a corner and when you are on the bend, flex your horse's head so you can see it's left eye (flex to inside). Right leg back then ask. If that doesn't work turn your horse into a large circle and very gradually make it smaller, that should make the horse naturally switch.

I have a hard time to "feel" leads. So I have to look. Watch the shoulders and whichever one is reaching further is the lead.

For walk to canter, you really need to have a responsive, forward and willing horse. Work on tons of trot to canter transitions. Try to make sure your horse isn't speeding up it's trot before the canter. Lunge your horse to teach it the verbal canter cue, reinforced by the whip if needed. Tons and tons of transitions in the saddle. When I ask to walk from canter I put my outside leg back, and push with both heels while tilted my pelvis forward and making a "kissing" noise which is our cue to canter. It takes a lot of practice. But I kept at it and can canter from a stop now.

I thought that was how you tell canter leads :P thanx heaps :P she is a forward and willing horse and will go at the speed I want her to from trot to canter. She can go from a VERY collected trot into a slow, on the bit canter, so I feel she is ready to do the walk to canter. Or verbal canter cue is "hop" (dont know why just easy to say) and to make her canter (to the right for example)on the correct lead, I put my inside leg on the girth and my outside leg behind the girth and tip her head into the center. It works and she gets on the right lead going right, just going left we need help and practice with....
Thanx for all your help, its very apprecaited :P

Your welcome! Good luck!

The other thing you can try for getting the lead is side pass the direction you want to go before asking. The first step the horse makes is with the left leg if you are going left. This will help them understand over time what you are asking when asking for the canter. This does take longer then other ways but works really well.

Ok I will try that as well. She side passess good so that's a head start :)