Stronger Lower Back = Stronger Core
Whether you're a beginner or advanced lifter, it's important to remember that you're only as strong as your weakest link. Don't forget about often neglected muscle groups such as the erector spinae (lower back). Direct attention will help balance out your core's strength and stability, thus improving the efficacy of major lifts such as deadlifts, squats, rows, and well.... just about everything.
Hit the back extension machine or try barbell good mornings at the end of your workout. Start with 2 sets, aim to nearly reach muscular fatigue between 15 and 20 repetitions, then work your way up from there.