Better teachers and better education is a problem that has lots of factors of which I'll only address the ones that I care about. This mostly pertains to elementary education majors.
1. The average education major is less academically capable than your average college student.
I'm sort of bending the findings of a study from about 15 years ago:
The Academic Quality of Prospective Teachers: The Impact of Admissions and Licensure Testing (warning this is a link to a pdf).
There are exceptions, those going into to teaching science or math have just as good a scores as math or science major. If you start off with poor talent it won't get much better no matter how good the training.
2. We pay teachers not nearly enough money.
If we really value education we need to pay them more. We need to be willing to pay the taxes to support the important job they do. Every good engineer, scientist or mathematician probably had a good teacher some time in their life. Too bad there aren't more.
3. We need better metrics to define what a good teacher is.
Don't get me started with the fiasco that is No Child Left Behind. Poor testing, poor accountability and poor funding.
How about to test a teacher's effectiveness we compare apples to apples. Let a teacher stay with a group of students for 2 to 3 years. They we can better tell if it's the student or teacher. If that doesn't work how about comparing the student's progress instead of the group's progress (which my wife thinks is a suggested change for NCLB), you will also need to control for similar groups (smart kids vs. smart kids).
4. Get rid of bad people earlier in the cycle (mostly at the college level).
I think this applies to all majors. Weed-out courses earlier. My major back in school (aero engineering) had to take an electrical engineering weed out course our sophomore year (don't ask me why). It will make you think twice if you want to pursue a major.
I think for teachers they need to take a public speaking course early on. If you can't talk in front of a class of 20-30 peers you certainly can't do that in front of a bunch of unruly kids. I get this idea mostly from my wife's experience as an instructor in a school of education (teaching teachers how to teach basically). Most of the kids have a horrible time teaching a lesson and this is as juniors/seniors.
Hell, even better give them a taste of teaching no later than their sophomore year. Most don't get that until their junior year. By then it's too late for them to do anything but finish their degree. This means they either will go into the system as a lousy teacher or flail around with a degree they don't like or can't use.
Extra bonus crazy idea.
Treat teachers like doctors/trade crafts. Extra training and lots of practical experience before we unleash them by themselves. Basically after they get their initial degree/license they will need to work with another teacher (like a residency/apprenticeship) before they get to pass another examination and get to teach on their own. The downside this would be rather pricey. Depends if you think education is important or not.
Extra bonus rant:
I think students, college students at least since I work on a university, are less capable than 15-20 years ago. The top 10% are amazing probably better than the top 10% of 15-20 years ago. The bottom 10% are the bottom 10% and it doesn't matter too much if they are better or worse. The middle 80% just seem less able to do the work and understand the content of most college level degrees. I've asked many people about this observation (from professors that have been doing this for decades to students themselves) and their answer has generally been yes. I do submit the caveat that the plural of anecdote is not data. So take all of this with a block of salt.