So I just got Meguiar's Cleaners Wax and it's my first time waxing.
I'm going to completely hand-wax my car myself. Should I wipe the wax on in a circular motion or back and forth?
Any other tips?
There is no "Rule" that says you have to do it a certain way. It is best to follow the wax manufacturer's directions.
Most people apply with an overlapping circular motion to ensure the application is uniform and complete. From my experience, wiping back and forth can miss some spots.
As others have said there's no specific requirements to the motion used to apply something like cleaner wax - the important thing is that you get a good even coat of the wax on.
This is generally easier to do with relatively tight circular motions and you can usually get a more even pressure this way as well. Depending on the consistency of the wax and the type of applicator used sometimes a "back-and-forth" motion can result in uneven pressure and potentially even a bit of pushing the wax around the paint surface rather than "applying" it. As a "cleaner wax" you want to be using a little more pressure than you would with a traditional sealant-only wax but it's still not massive amounts.
As Paulster mentioned in his comment there is much to be gained in the preceding steps pre-waxing (Apologies if you had already considered these and were merely leaving them out of the question for brevity but to get the best out of the process), ensuring the paint surface is as clean and smooth as possible will make a big difference to the end result. I don't want to go too far off topic here but in general you should:
If you want any further explanations or detail on any of those steps post them in separate question(s) and I'll be happy to go more in-depth.