We started at 2.5 after months of him practically begging us to potty train. We followed Gina Ford, and while he got it in principle, it was a couple of months before we stopped having regular accidents. 5 months later and he takes himself to the toilet for both 1's and 2's, although he of course needs help cleaning up. He still wears a pull up at night and we're nowhere near ready for nighttime training.
We did train over a week in summer when his nursery was closed, and we were home with no real plans. His nursery played a big role in teaching him alongside a group of other toddlers at the same time.
For months before we started training, we would have him do a wee in the potty just before getting in the bath because he consistently did one at that time. At one point, DH moved him to the toilet for the pre bath wee. I was amused to find out that involved standing him on the seat of the toilet and having him aim down into the bowl. I thought he was crazy, but now its sheer genius in public toilets. There are no worries about his precious parts touching a nasty public toilet! And his aim is remarkably accurate. Highly recommend the technique.