I try to add variety to my practices. I also know that its not the quantity, it is the quality of practice. I shoot progressive drills and I work on my patterns on a daily basis. I also practice mentally by using visualization techniques... some think that's weird, but it is one of the ways I strengthen my concentration and focus. I try to prepare mentally and physically, and I try to keep that balanced.
I also shoot a lot of rotation, straight pool, and the ghost. If I am preparing for a 9 ball tournament, I'll break, and then set balls 10-12 randomly on the table after the break and start shooting. After I become proficient at running out I will do the same by placing balls 10-15 randomly on the table after the break shot. After a while I will eliminate the extra balls.
I also play a lot with other players and I teach. While I am teaching I am also learning. I never take the approach that I am "better" than any of the players that I work with. I try to remember where I come from, which is being a kid with a lot of questions and no answers.
Learn to not practice "routines". Routines are boring and tedious. Add variety and always challenge yourself during practice. Learn to trust your stroke. Most of the shots you will miss will be due to you talking yourself out of them. The other shots you will miss will be due to excessive body movement. All that should move is your shooting arm from the elbow down. Learn NOT to make excuses. Some days are worse than others, just make sure you show up the next day willing to improve. The best players have an insatiable love for the game of pool. They play through the good times and they play through the bad times. Champions understand that there is always something new to learn and they never rest upon their past accomplishments - they always prepare for the next battle.