Hi Jen,
I don't want to be the voice of discouragement here, yet I think initiating toileting for a child this age is choosing to create a difficult challenge for both yourself and your little one. Believe it or not, there are advantages to having two in diapers. (As a nanny, I know this personally. It's easier to deal with two diaper changes than to be cleaning up accidents and tending to a baby.)
My personal opinions aside, here's a resource I highly recommend.
http://www.betterkidcare.psu.edu/AngelUnits/OneHour/Toile...
This article was created for the early childhood ed program for Penn State, and has a list of assessment questions, which will help you be best able to evaluate if your child is ready to start.
In my view, assessment is your best ally in helping your child learn how to use the toilet successfully. I like to think of it as if you were teaching a child to ski: you would make sure they had all their equipment on before sending them down the bunny slope. Likewise: proficiency in the skills they list will give your child the best possible chances for success.
One philosophy a few of my colleagues and I have come to acquire is that a child has their own developmental time frame for learning how to use the toilet. We can start earlier, but if they aren't ready, it will take us just as long (In their lives) as it would if we had waited until we saw true readiness. Thus, a child who is going to learn to use the toilet at 2 years 7 months will still 'get it' around this time, no matter if they had started at 22 months or at 2 years, 5 months. Waiting until readiness eliminates more frustrating accidents, because when kids aren't ready, they just aren't. Nothing we can do will change that with long-term effectiveness. This is why you hear stories of children who did fine with m&m rewards for a month or so, and then began having accidents again.
The philosophy around toilet learning, too, might seem a little unfamiliar. Let me assure you that this isn't a bunch of touchy-feely theorhetical mumbo-jumbo. I have helped children with learning to use the toilet for nearly 20 years now, and have seen this developmentally appropriate approach facilitate far more success-- and sooner in their process-- than more conventional approaches. And here, I'm not saying there's anything horrible about more conventional approaches, but the fact that it is a frequently-problematic process (as evidenced by the number of these posts I see) can't go unquestioned.
In our home, my son was allowed to wait until he showed readiness. This was when he was about 3 years, 3 months. We offered him cloth diapers or cloth underpants to wear, and paper diapers at night. Two months later, he was in underwear overnight. We've had one wet bed accident since then and virtually zero power struggles around toileting. (Occasionally he doesn't want to use the toilet, but that's pretty common... we just tell him to go try anyway.)
Sorry this post is so long. This is something I feel strongly about, though, and I do plan on offering classes in my area starting next autumn. Parents have a lot of challenges with helping their children learn to use the toilet. Funny thing... if we let it be our child's journey to figure out, and just provide great support, we make this a more positive process for everyone involved!
Best to you,
H.