Technically, generating a barcode takes about ten seconds — type a number, pick a format, download. The part that actually takes thought is everything before that click, because a barcode reprinted after a batch of products is already on the shelf is a genuinely annoying problem to have.
Pick your format first, not last
Selling through physical retail? You'll likely need EAN13. Managing your own warehouse or shipping labels? Code128 gives you more flexibility since it isn't limited to digits. Decide this before you generate a single code, since switching formats later means reprinting everything.
Set up a numbering system you won't outgrow
If you're assigning your own internal codes (not registered EAN13s), leave room to grow — starting at 00001 with five digits handles up to 99,999 products, which is more headroom than most small businesses will need for years.
Match the size to where it'll be scanned
A barcode scanned by a handheld scanner a few centimeters away can be smaller than one meant to be scanned from further back, like on a large box. Print a test at your intended size and scan it before running a full batch — this single step avoids the most common barcode complaint we hear, which is "it printed fine but half of them won't scan."
Print on the material you'll actually use
A barcode that renders perfectly on a laser printer can blur slightly on a thermal label printer, or vice versa. Always do a real print test on your actual printer and label stock, not just a screen preview, before ordering a large batch of labels.
Keep a record of what you've assigned
Even a simple spreadsheet mapping product name to barcode number prevents the awkward situation of two products accidentally sharing a code, which happens more often than you'd expect once a catalog grows past a few dozen items.