You don't have to make HUGE changes to "shock" your system. You can do small things to mix things up. For example, do weights before cardio (or vice versa if you usually do it that way already). Do abs first instead of last. Add some pilates or yoga. Or train differently. I usually do total body workouts each day I train, but I could switch to doing upper one day, lower the next day to vary my routine. Or, you could concentrate on cardio one month, then concentrate on strength the next, yoga the next, etc. Another way, is to change your intensity. You could do more reps with light weights on month, then fewer reps with heavier weights the next. Same goes for cardio. You could train at the top of your HR zone one month, then do low fat-burning the next. You can still do the same things, just mix it up a bit.
Hope this gives you some ideas, without confusing you even more.

Carole