Proverbs 25:28 He that hath no rule over his own spirit is like a city that is broken down, and without walls.
Ruling your spirit talks about your controlling your spirit or having self control. Without self control you are like a city with no protection against your enemies. Satan and sin will have full access.
As a born again Christian you want to yield the control you have been given to the Holy Spirit. As a lost man you really were the slave of sin, without much control over yourself. Now you are born again and have control but better than trust your own ability, yield your self in obedience to the Holy Spirit.
The biggest problem any of us have in life is not caused by the devil or others. We are our own biggest problem. Exercise some self control or even better some Spirit control!