The biggest mistake I made was being too excited to start printing things so I didn't properly level my build plate. That caused lots of frustration later down the road. S3D has an amazing bed leveling wizard under the tools menu. Use it two or three times in a row until everything is perfect. However, that requires connecting your printer to your computer which is kinda tricky if you have windows 7 or above (I can post directions later today if need be).
The other thing I have come to realize is that 3D printing is a lot more of an art than a science. I find that I am tweaking my print setting for almost every print. In the beginning I printed lots of things multiple times just to see how different settings work out. Now a year later I am a bit more confident but every once in awhile I still have to reprint things so don't expect magic over night. Luckily for me it is very much a hobby so I just enjoy the ride! I'm sure you will too.
Lastly, I have found this forum to be incredibly helpful and friendly. I highly recommend keeping a close eye on it because you will learn all kinds of things.
EDIT: Here is a link to another post that explains how to connect your FlashForge Pro to a windows machine in case you need it.
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