Any tips on how to make the eVisa process as smooth as possible (for Americans)? In particular:

1. photo-taking - using a phone? Do I just stand in front of a white wall? any tips on getting photos accepted?
2. I read on this thread that max. of 20 countries can be entered, but it is not necessary to be 100% accurate, right?
3. do most people get their eVisa approved and emailed to them within 24 to 48 hours?
4. anything that is likely to trigger an error?

Thanks.