We choose family significance for middle names, but I don't think that's important. I do personally like a story behind a middle name though. I just think it's more interesting than being just a name you like. You be a lot less conservative with a middle name choice, so I like if it has personality. You could use the name of a vacation destination, or city or other place name that means something to you or the name of a movie star you both admire. Maybe a flower from your wedding bouquet, the month you met or married your DH, or even your favorite season (these would prob work better for a girl)
One thing that's a little TMI in my opinion is giving your kid a mn that relates to where or when they were conceived. No kid ever wants to relay that story