I started at 2 years 9 months and took three days off work. I waited until she was regularly having long periods of a dry nappy, was going off to hide to do poos and could tell me that she had done a poo. And she had the physical strength / co ordination to be able to pull her own trousers down. Without those things, I think it would have been tricky.
Naked from the waist down Day 1 and we stayed in the house, and as soon as she started weeing, just a clear instruction of "wee goes in the potty" and place her on the potty, and point at the potty so she could sit on it, and I just kept on doing that over and over for the first day or so, and talking loads about wees. Loads of accidents of course on the first day or so, but by day 3 she very much understood the sensation and could go to the potty by herself for wees. By the end of the first week she was reliably dry. She was quickly dry at night after that, though that is variable in children and isn't always linked to day time control.
I ignored advice to just keep asking your child if they want to go to the potty etc. I found that questions like that raised anxiety in my daughter and instantly she got defensive and refused to do things. They don't know the answer to that question yet. I felt my daughter needed very much to feel that she was in a situation where the adult had everything in control and was calm, and would help them and show them what to do. Not a situation where they had to be telling the adult what they want to do, when they don't know how to do it yet. Too much pressure and uncertainty for the child.
Poos took a bit longer, perhaps a week or two. After meals I would take her outside and when I saw the warning signs of her needing a poo (like wanting to make an exit / hide) I'd just say very clearly "Poo goes in the potty poo goes in the potty!" and point to where it was, and she'd run over and do it eventually, with huge celebrations and singing / dancing afterwards from me. Quite a few poo on the floor accidents before that, but nothing we couldn't handle. Its better they learn to just expel things and have an accident rather than hold onto it and become constipated / frightened to release. You have to just create an atmosphere of...everythings ok...accidents are not an issue, everything is fine, Mummy is calm, Mummy has everything in control and will show you where the potty is, you're doing great, we are learning together and so forth.
It also needed my complete attention and focus for three days to get it done. It was all consuming for those three days and I think I would have struggled to do it if I had other things going on in my life at the same time.