Many people go to the gym and do the same stuff over and over again. When you're new to training your body can change a lot doing that. As your training age increases (the amount of time you've spent training), the harder it is to make progress. The great news is, you can easily continue to make progress by changing little things. And no don't call this "muscle confusion", call it progression.
The first thing you need to do it choose an exercise you are doing. Let's look at a few...
The Plank, first off there are many different versions of how to do a plank properly, I will not get into that discussion at this time.
The easiest way to progress is more time spent in the position. But you probably knew that. If you feel that you aren't being challenged doing a plank for 30 seconds move to the next progression.
Hold the plank position but take one foot off the ground. By changing the base of support you change how the core and other musculature has to work. You can also do this by taking one arm off. You can then from that position increase time until you another challenge. How do you make it harder from there?
Put your arms on a physioball. Then increase time again. Then take one leg off the ground when that become easy.
And so on.
You are still doing a plank you are just continuing to challenge your body.
How about a cable row?
You start off doing cable rows in the seated position. Does that feel easy?
Try doing them standing. This will challenge you because you have to use more muscles to accomplish the same thing!
Did them standing for a while, and they are getting easy, try one arm at a time. You will have to use your core to resist the rotation the the cable will be trying to cause.
Is that getting easy, go back to two arms and now just one leg. Now a whole new level of balance is being taken into account.
What about 1 arm and 1 leg?
Here is a chart to help you with some ways to progress your exercises:
As you can see there are many ways to continue to challenge yourself and continue to make progress in your training. Make sure when you do move to the next exercise you truly have control of the previous, if you don't it will probably show when you progress to early.