We cannot avoid sin in ourselves no matter how much will power we exert.
If this is true then Jesus is not a very loving person. It is not loving, caring or kind to tell someone to do something that they cannot do. Jesus told the woman who was drug out to him for committing adultery to go and never sin again. How cruel it would be to say those words if she, who had not the Holy Spirit dwelling in her, could not actually preform the command.
Your will power is necessary to avoid sin. As you say, we need to think on that which is good, the bible confirms this. Your will chooses to think on something else by the spirit of your mind instead of the carnal mind. These things are all possible through a proper use of the will applied through the direction of the word of God. As Jesus told Nicodemus, you must be born of the spirit as it is the only way to avoid sin. He wasn't speaking of the Holy Spirit as he expected Nicodemus to know this already being the teacher of Israel. The Holy Spirits indwelling ministry wasn't going to start for another 3 years.
A proper use of your will is different than will worship and should be seen as such. Willing to be molded into the image of Jesus by the word of God that reveals to us who he is so that we can willfully walk as he walked though the knowledge of his person. Purifying ourselves as he is pure. As Peter said, we need to read the scripture and take heed of what it says until Christ be formed in us. The take heed part refers to our will to be like him.
In Jesus Name,
Gary