I would suggest you to do it while the weather get warmer, then take off the diaper, not to wear it in the daytime at the beginning.
My method was bought a cheap-cheap 痰罐, then instruct my daughter go to sit on it (like in every 2 hours), also put some toys around 痰罐 to attract her to sit still. Try it in a continuing basis, my daughter then learnt to 痾 in 痰罐. But you must be patient because there must be 賴濕 occasionally.
Even 賴濕, remember never discourage the kid, just not to scare him or her. Also praise the kid once succeed, it works on my daughter.