We did it really slowly. DS was over 3 before I really started to TT. We went straight to the toilet using an insert seat thingy to make the seat seem smaller for DS.
I would really only put a pull up/nappy on him for his nap or sleep at night. At first he would wee sitting down but OH taught him to wee standing up by doing it with him outside and in the toilet. He didn't really stand up until he was tall enough to reach the bowl (ITMS) and we TT at night mnths after day TT when he really had that down pat.