Summer is approaching and that means only one thing for makeup: smearing. High temperatures and running around doing errands will cause your makeup to melt faster than ice cream on that same day. 
Although it may seem impossible to keep your makeup in place (so impossible that many people avoid wearing makeup at all during hot days) there are few tricks to keep your face looking fresh and smear proof. 

Use a face mattifier. Good face mattifier is a perfect base for makeup and will keep oil at bay even in the hottest weather. 
If your face is well matiffied it's unlikely for the makeup to smudge. My favourite is Murad oil-control matiffier. It also has SPF 15, another summer day necessity.

Prime your face. I used to think using a primer on a hot day is too overwhelming for the skin and that last thing I need is a thick layer of added product to block my pores. 
Over the time I've learned primer will actually help you by keeping the makeup in place and making it look nicer even if you get a bit oily. That added layer is not too much if you pick light primer that you can't feel on the skin, like Prime Time from Bare Minerals.

Use the lightest foundation you possibly can. That means no liquid, cream or mousse foundation, powder foundation is your best friend. 
Liquid and cream foundation will clog your pores and look weird when the face is oily. 
Also, use very little powder, only enough to cover the face, don't apply more layers. Most people add more makeup thinking it will last longer, that way you'll only make the face look cakey. 
Even if your face starts to look oily, under thin layer of powder it will end up looking dewy. 
I am using my favourite powder Mineralize skinfinish natural from MAC, but any other powder will work. Maybelline Fit me Pressed powder is also a great choice. 

Set the makeup. Use a setting spray you can trust. Most of them these days are designed to lover the temperature of the face (don't ask me how). Urban Decay All nighter Makeup setting spray is one of them with its ''temperature control'' technology.

Blotting tissues are your friend. If anything else fails, blot. Always carry blotting tissues in your bag, so you can use them if you notice any additional oiliness. I've been loving Oriflame Optimals Matte touch face blotting tissues, they work very well and are not expensive.