I like to think our goal in every practice session is not to get to the next level, not to progress faster through the repertoire or techniques, and not even gain mastery over what we already know, but to just to keep it fun and interesting. During the practice session I've come up with a system (working for now, probably won't last forever) where for each smile, "OK Mommy!", and task performed with a good attitude, I put a pony bead into a jar. At the end of the session, we count the beads.
Note I don't put a bead in the jar for every task done or every repetition of something. If she doesn't do something with a great attitude, she doesn't get a bead. Some short practice sessions she'll end up with 19 beads, and some long ones she'll only get 5. She gets a bead if I say "OK, rest position" and she comes right over without me having to ask twice. She gets a bead if she tries really hard on a particular task, especially if it's difficult.
What do we do with these beads? For each one she gets one minute of computer time. I've found a really great website for kids that teaches phonics, math, telling time, pattern recognition and many other things. A lot of it is free, but I'll probably be upgrading soon because it's amazing. It's called Starfall. I love that her reward for practicing is educational!
When we don't have our computer, like when we travel, she gets the same amount of time on my iPhone. I don't tell her what she can and can't do (there's nothing inappropriate on there) but she always picks the same app: Timmy's Kindergarten Adventure. Same idea. Cool educational program that she loves to do and is motivation for having a great attitude