1. Don't wear a matching tie/pocket square combo. Never ever.
2. You can wear it as a simple folded square or use a multi-peaked fold. With the silk or sheen varieties, there are all kinds of ways of wearing it in a puffed fashion.
3. Use a solid color--probably white--in a simple cotton or linen. Some would say there is some utility to the pocket square: It's basically a handkerchief in your pocket. If you wouldn't blow your nose with it if you needed to, it's probably too fancy. Silk ones (usually worn puffy) can be overstated and they definitely have no utility, but can be a smart look and are usually more conducive to incorporating colors. The simple white square is a classic look, but as you can see in the pictures, it's also modern when coupled with a streamlined suit. You can get work stripes or patterns in if you dare.