You don't need to take all the exams at once so it's worth planning the order to revise for them in.
Generally, flying schools require a student to pass Air Law before they can undertake their first solo flight. For this reason it's a good place to start, so that ground school doesn't slow down the actual flying.
Apart from that there's no set order, however it's generally considered that some exams are harder than others and that it's better to group a "hard" exam with one or two "easier" ones. Some also have overlapping content so it makes sense to take them closely together.
Our suggestions then are something along the lines of:
- Air Law, to make sure there are no barriers to the first solo flight
- Operational Procedures, as much of the content overlaps Air Law
- Human Performance, which is considered one of the easier exams
- Communications, as you'll be learning a lot of the content as you fly
- Meteorology, which is one of the bigger subjects
- Principles of Flight, which is less demanding
- Aircraft General Knowledge, because it overlaps with Principles of Flight
- Flight Performance and Planning, which you will be learning about during the later stages of flying
- Navigation, for a similar reason, and should help you to prepare for the solo cross-country
The last two are quite big subjects so you may want to tackle them together once the rest are out of the way.
The above order is just a suggestion but let us know if you find it useful, or find an order that worked better for you.
And if in doubt: ask your instructor!