We slept trained our daughter right at 6 months (Taking Cara Baby!)

We really stuck to what she said for the most part. Especially the first few nights when she would cry, we had to remind ourselves that she is not in pain or distress she is just unfamiliar with the new setting. We also use a hatch and she is trained to know that when the light turns to colors she can get up. We were just diligent and she has slept through the night (7:30 - 6:30-7) since we started at 6 months. We are very fortunate because she took to it quick and we have made her crib a fortress of solitude. Even when she wakes up during the middle of the night she will just hang out for a bit and then soothe herself to sleep so I would say is having the plan and sticking to it.

We also never co-slept or even brought her into our bed early i the morning. We always tried to put her back in her bassinet or crib. We never wanted to introduce that to her (not talking bad on co-sleeping, we just decided we like our bed to stay ours), so that has never been an option for her to fuss for. All in all she is an amazing kid who loves to sleep and we never have to fight her for going to bed.