Practice and lots of said practice. The gallery level miniatures that you see used in marketing material are often completed at the hands of painters with years of experience and hours upon hours of effort per each miniature. If by chance you simply do not wish to put this effort but still want an awesome looking miniature we suggest looking for a local artist to commission a piece or check out the Reaper Miniatures Forums to see if a project can be completed and shipped to you directly.
Should you desire to take up the hobby and want to gain the miniature painting skill yourself the best first step is to start with the Reaper Miniatures Learn to Paint Kit Core Skills. From there the Reaper Miniatures forums have developed a great community to help expand your skills and guide you in mastering this particularly rewarding hobby.
The Craft: Articles all about painting, basing, and conversions written by pros and fans.
The Craft Corner: A little section of our forum where you can show off your paint jobs and get criticism, ask questions, and meet the friendliest painters on the internet.