Since I have normal-dry skin, I have stayed away from using powder foundation. However, in the summer when it is a bit more humid, I find powder foundation to actually be nice. It feels lighter, I can control coverage, and it feels better in humidity than a liquid foundation or BB Cream.
Hopefully, I can give you some tips on how to wear powder foundation because I know that it's kind of intimidating! Before, when I thought of powder foundation, my mind directly associated powder = dry. Blegh. But that's not necessarily the case. I've really fallen in love with this routine because it makes the skin look so healthy, natural and even.
First, primer. It's important because the powder foundation won't buff as well over just moisturizer. I use Prime Time from BareMinerals, which has SPF 30. I actually included this in a "Disappointing Products" post sometime ago... I found it to be very slippy to use under liquid foundation. It sat unused at the back of my bathroom cupboard until I tried it with powder foundation. It has a bit of a tint, so it's actually nice to wear on its own, and it leaves the skin silky-smooth, which is perfect for buffing in powder foundation.
The brush I use to apply is the Real Techniques Buffing Brush, and the powder foundation I use is the classic BareMinerals Original Foundation, which has SPF 15. Between this and the primer, you have your daily sun protection sorted. The foundation is a loose powder, but it's not messy at all. There is a plastic thing you turn around inside the product to control how much powder you dispense. The best thing to do is put a bit on the brush, swirl it around on the cap and tap off the excess. Then buff.
I continue to add the rest of my makeup, and then move to this last, essential step. To finish off, I use a facial mist to set the powder and add dewyness. I found this Argan Oil In Water mist by Korean brand The Face Shop for only 15 dollars. It is a moisturizing spray, so it sets the powder foundation beautifully, removing any look of "powderyness". It is the perfect finishing touch!