If there's one thing you do, makeup-wise, before leaving the house, it should be putting a touch of concealer at the inner corners of your eyes. As I've said before, just getting rid of the darkness there wakes up your whole face and makes you look prettier—even if you don't wear a stitch of anything else. (Well, I hope you're wearing clothes, obviously.)
Lately I've been loving this Eyelid Primer from Canadian line Pandora's Box because it not only primes your lids for shadow application, it also doubles as an eye-area concealer for fair or medium complexions. I'm not really sure if you're supposed to use it that way, but I'm finding it works great both all over my lids and at the aforementioned inner corners. It has great "slip" (probably due to silicones, which I'm okay with in that area) and then dries down to a nice, matte finish.
Even if you don't do the concealer thing, I still recommend it for helping your eyeshadow to stay put—especially for summer. For more hot-weather (and/or oily skin) makeup help, check out these tips that Pandora's Box founder Susan Kirsch shared with me back in November.
Available now at Murale and pandorasmakeupbox.com.