Don't EVER put product onto your hand and transfer it to your face (like many people do with concealer), it is very unsanitary. Instead take an old DVD/CD, a blank CD/DVD or an old itunes card (or any type of gift card with a flat surface). Make sure you wash it well and use that as a pallet like an artist would use a paint pallet. For a DVD or a CD use the bottom of the disc, not the top. It is a more sanitary method to putting on makeup and it keeps you from getting product all over you and making a mess.
I learned this tip when I was in cosmetology school where they said to use a DVD/CD. It works great, I use it every single time I do someone's makeup. Some of us (like myself with my personal train case) may not have enough room for a disc to fit in our makeup bags or train cases. This is where I recommend an itunes card. It works just as well (using the top of the card) and it is more compact.