1. Wash your hands!
I carry an anti-bacterial hand gel which eliminates the need for soap and water so I can sanitize my hands on the spot. I find it also puts the client or model at ease when they see me being hygienic from the start.
2. Scoop, scrape or squirt products onto a clean palette
By working from a clean palette you cant double dip which can contaminate the product. You can use a spatula to transfer cream or loose powder products to your palette.