Because every printer's capabilities are different, it is best to do a test run. This will allow you to adjust your printer's margin settings, printing resolution and image placement.
If you will be creating a lot of wrappers invest in a paper trimmer which you can get from most office supply stores. Trimmers usually cost between $15 - $20 and will cleanly trim your wrappers and save a tremendous amount of time.
Using printer ink can be costly, especially for wrappers with intense colors. If you will need a lot of wrappers, save ink and cost by printing one set of wrappers, then run off color copies at your local copy or office supply store.
Create unique edges on your wrappers using fancy edge scissors found at most craft stores.
If using glossy photo paper for your wrappers, you may want to spray your finished product (prior to wrapping the candy bar)with a clear acrylic spray (available from any craft supply store). Black ink will smear or wipe off glossy photo paper even when dry. To correct this problem, just choose the darkest blue setting, it won't smear like black ink and you can't tell it's not black.
