Live by Example
When child tries to test boundaries and father accommodates this...reaffirm your bounders this is letting them know you have limitations and that's where you draw the line. This is done on regularly basis ALWAYS. Rewards are done on a more irregular schedule. Rewards are much needed but, to keep its freshness don't over use them.
Always be an example...remember who you are. You are the one who is involved with the parent of that child...you must have done something good. Every thing should be done with Love for others and not for personal gain.
For single parents remember your relationships are examples of how your children will perceive how to treat the other significant other or yet how to be treated.