If you want to make your foundation last longer you have to remember: oil and water don't mix! Have you tried to mix oil with water in a glass? It's not possible. So...
Water based primer or facial creme goes with water based foundation.
Oil based primer or facial creme goes with oil based foundation.
Don't build up a lot of products. Use a primer or a facial creme before applying your foundation. If you have super dry skin, like me, you can use more products.
If you want to, you can use a translucent powder to set the foundation. But wait a few minutes before you add it. People with oily skin will benefit from this.
And for Danish readers/Og for danske læsere: Jeg har lavet en lille video på youtube om dette. Følg linket her.