If you have to ask then don’t engrave them. Engraving your wedding rings is like getting a tattoo -- it should be something important, meaningful to you and not some trendy thing you read in a celeb tabloid magazine.
Simple options are your names, wedding date, a quote or lyric that has meaning to you and your fiance.
When choosing wedding bands ask what your engraving options are regarding character count and find out how long it will take to have the engraving done. As long as you aren’t in a rush you should take some time to think about what you want and if you can’t think of anything don’t engrave them. You can always go back to the jeweler and have them engraved after the wedding.