Should I be thinking about parenting skills when my child is nine to twelve months old?

Yes. Parenting starts before the child is born. The parent-child relationship is the foundation for the child's development. The parent influences the child and the child influences the parent. Your attitudes, behaviors, and emotions impact the child and vice versa. Become the best that you can be in every way and share yourself with the child. Grow with your child.
A little earlier. I encourage putting baby in his own crib, drowsy but awake, without a pacifier, at a consistent time, after a routine that includes reading & wiping out baby's mouth after the last feed before 5 mos. Habits are set between 5-6 mos. Learned behavior starts @ 6 mos. When he can understand a firm, low, no.If you re-direct him @ 6 mos. For unsafe behaviors, he'll inhibit to no by 9 mos.
Yes. As your baby begins to walk and seems to understand the word "no, " it is easy to expect too much from them. The main job for a parent is to teach. Teach the child what you want them to do. The early toddler years are marked by confusion and an uneasy blend of dependency and emerging independence.