Some topics lend themselves well to being done (studied and sat) together.
Air Law and Operational Procedures used to be a single subject - they interrelate and you may as well do them both together. Many schools will insist (for no real reason...) that you have passed your Air Law before you go solo, so that may also be a reason to do it early. Finally, many people find it the most annoying - another reason to get it over and done with.
Human factors is very short and I think most people find it easy. Do it whenever you want - add it to the same sitting as the law subjects if you can.
When you start doing cross-country flights, you will start using RT and you should also start to do some Met and Navigation, so that's a good time to do those. I think it makes sense to wait a bit with these until you've actually done some XC, which will give you a better understanding of why you are meant to learn what you are meant to learn... Met can be quite chunky, so I'd begin with that, then add Nav and RT in that order.
Finally, the Aircraft General Knowledge and Principles of Flight also used to be one exam - bundle those together with Flight performance and Planning as they fit together. Again, you should have picked up a large part of this from your instructor over the course of your lessons, so there is little to be gained by pushing through with them too early.
Your first W&B on the aeroplane you are using for your lessons may well be an eye-opener!
Have fun - learning new stuff should be fun as well as necessary. If you find that another order works for you, good for you - come back and tell us about it!
B.