What are you concentrating on when you hit the gym? Everyone has their "favorite" thing to do, and of course it's something that they are strong at.
Unfortunately that often results in overtraining a specific part or area, and/or unbalanced development.
You've all seen examples of this - the guy with the huge upper body and toothpick legs is one classic example, and the twig of a girl who never gets off the treadmill.
Worse yet is someone who constantly works their chest and not their back, and gets the shoulders that are rounded forward, or the bicep guy who's arms are 'permanently' bent front.
Not only do those things look bad, they also effect their musculoskeletal connection.
One area that often gets overlooked is core fitness.
Or people just do sit-ups, looking for those six pack abs (which doesn't work, by the way) and they neglect their lower back and obliques.
So we all (I include myself) sometimes focus on the parts that make us feel good about ourselves, but we have to break that mindset to become the best we can be.
This actually has a dual meaning, changing your lifting routine, the first is that we have to spend more time on parts that we have been neglecting, so think about that.
I just starting spending more time on my rear deltoids (back part of the shoulders) because I realized all my shoulder exercises were overhead lifting or front dumb bell raises, and I was pretty much totally neglecting the third 'head' of my shoulder muscles.
So that brings us to the other half of this equation.
Not only do you have to do more for your neglected muscle areas, you also have to think about different exercises for all your lifts, so you challenge yourself.
As I've stated many times, the human body is incredible at adapting to a routine, so you have to regularly shock it with new routines.
Don't think you are limited to a few possibilities with a muscle.
For example: Biceps - not just dumbbell curls, but preacher curls, standing curls, barbell curls, cable curls, incline bench curls, reverse grip curls, etc.
You are only limited by your experience, so look around you (and here) for different options.
I would also encourage you to look around the gym (if you're at a gym) and see what other people are doing, and asking questions.
That may seem awkward, but most people are happy to talk about their exercise regiment.
It gives them a chance to "show what they know" but take their knowledge and then check online for proper form and further information.
Hope this helped you think a little differently about your routine.