Start by using a base for all products you plan to use. A primer for your foundation (and try Revlon Colorstay Foundation, that product STAYS PUT!), liquid blush under your powder blush, a primer for your shadow and color your lips in with a liner first then apply lipstick or lip gloss. That should already help your makeup stay a longer than it would before.
Make sure you use waterproof mascara (We have a review on the website for Urban Decay "Cannonball" mascara http://beautymarksthespotreviews.weebly.com/2/post/2011/07/cannonball.html) because if your sweating or in the pool, you dont want your mascara to run! Also waterproof eyeliner will hold out a little longer too (and dab black eyeshadow over it to help it stay put) Lastly, if you don't want to wear a heavy foundation and just want a little coverage for the hot weather, I suggest using a tinted moistureizer with SPF in it to protect your skin :)