How do you open your box flaps with no creases?

[Gakken85]

Sometimes it comes open like a champ... sometimes it creases like a bastard and I say "oooof!"

Am I missing some obvious trick here? Sometimes I push the opposite side of the box forward to give it room to clear the tabs, and sometimes I use a plastic knife to jimmy it up.

[xstoys]

Use a letter opener to push the main flap past the 2 side flaps.

[Bub]

Same as xstoys. Letter opener.

[Benson13]

Thanks xstoys. I recently opened two boxes that way and it works great.

[Murphy]

untill recently ive been using a Swiss Army knife to open the way xtoys explained.

[Bub]

Most of the toy sellers in Hong Kong use either a ruler or a cutter.