Anyone with access to any 2 3DS's and one cartridge can do this easily.

1. Put your streetpass compatible game in a 3DS that does not have streetpass data for it.
2. Boot up your game and go to it's streetpass settings.
3. Once streetpass is turned on, the data will be saved to the 3DS itself. You can delete any extra (non-streetpass) game data in the settings.
4. If you have an extra game then you can gain benefit from the data in the extra 3DS.
5. This is super helpful because it'll help you and anyone the other 3DS streetpasses.

- Do this for every friend you streetpass often. Well, as long as they don't own the game in question or their streetpass slots aren't full. This can be checked in the settings.

- I personally find it hard to get streetpass achievements in Animal Crossing: New Leaf, Pokemon Rumble World, and the Plaza.

- Always keep the streetpass data for games you don't play/own anymore. Unless your slots are full, it is good to help others.

- Would anyone like me to post these guides on GBAtemp?
Tips for Getting More Streetpasses
Tips for Free Badge Arcade Badges

 

Its only meant to help those who use streetpass.

 

Thanks for the comment. C:
You can easily find HomePass (streetpass hotspots at home) and a list of games that use streetpass on Google.
I was just looking into HomePass recently and it doesn't look hard to do if you get the right wifi extender.

If you download enough games you may run out of room if you stick with the 2GB SD card 3DS' come with.