First, don't ask anything about their past life and past relationships. The same as other dating, it is impolite to ask anything about their past. For transgender women, dating is a new start for their life. It is also a new start for your life if you are seriously looking for a long-term relationship. It is impossible to meet an ideal partner if you always stay in the past life.
Second, respect your trans dating partner. Transgender people vulnerable group, they need to be respected and loved by all of us. When dating a transgender woman, no matter she is the one you want or not, be a gentleman and respect your partner.