(This is day 2 - she was still a little nervous to leave the potty for an extended period of time)
I did my research first, finding posts on Pinterest and other places online, and asking friends with kids for advice. Here are the top pieces of advice I found that worked for US and OUR kid:
1. Don't do it before they're ready!!
-your child should have some interest in the potty
-should be able to stay dry for a few hours at a time
-has words for #1 and #2
-can tell you before, while, and/or after they have just gone
Mallory had all these signs and then some.
2. Get a "potty."
I hated this idea but realized that we HAD to have one for her, especially in the beginning, because she needed to have a potty in the room she was in, and she is too small to get up onto the toilet without help if she needed to. So, I caved, and we got one (and I'm glad we did).
3. Stay at home - go pants-less - keep your kid on easily cleanable surfaces - and no tv.
We went without pants for 3 days, confined to the kitchen, and had a couple accidents. However, even when she had an accident, she would stop herself, run to the potty, and then finish going (another sign that we were doing this at the right time). Also, the no tv thing is crucial. She doesn't get to watch television anyway, but if Mommy or Daddy have the tv on while she's up she will sometimes get sucked in. It's important that she not have too many distractions on these first few days.
4. Becoming a "Big Girl."
Being only 21 months old, I wasn't sure if she would totally get this concept. On day 4 we decided to put her in some underwear. Right after we put them on her she came to the bathroom with me,(just because she likes to) and I thought, "Hey, I should tell her about Mommy's underwear." So, I showed her mine and then pointed to hers and talked about how she had "big girl underwear like mommy!" and she lit up like Christmas morning! It totally clicked at that point that underwear were a super cool thing to wear.
5. Continual reminders, but not badgering
The first day we were so paranoid we kind of had her living on the potty, and then day 2 SHE was nervous to leave it. After the first day I realized she was better at it than I thought so I encouraged her to move around. I made sure I put her on there every 30 minutes or so. After day 3 I realized she was good if I put her there every hour. If she didn't go then, after I told her to try, I would try again in 30 minutes and she would usually go then. Many places I found online suggest every 15 minutes no matter what. Mallory was super ready so she didn't need that. By day 3 she had started telling ME when she needed to go - not every time, and I still sat her there each hour but it was amazing progress.
6. Naps and nighttime come later.
Especially since she is so young I am not anticipating dry naps and nighttime for a while. It will come.
Bonus (conflicting) advice: Rewards
A few articles I read said not to reward or get overly excited about going on the potty. I totally disagree...kinda. We clapped and were very happy and she got a cookie (mini Chips Ahoy), each time she went. We were excited and so was she and it was fun to go on the potty. HOWEVER, after the first 4-5 days, already I was really pulling it back. I now still smile and say "yeah" but not as big, and if she doesn't think to ask for a cookie, I don't give her one. I do continue to emphasize what a big girl she is, going on the potty.
I know we will plenty more accidents along the way and that we are by no means done training. I also know that this is how it worked for Mallory, and that it could, and probably will be, very different for our other children. However, I am so pleased that she is doing so well, thus far!