The best way to get better is to ask the lady that you are about to go down on what she likes. Also be aware that you are poking around in the most sensitive area of her body. Whatever you do, do it gently.

You know what I sometimes do?  I ask the woman to fuck my tongue with her pussy.  I lay down and let her make the moves on my mouth.  As she's going about grinding on my tongue I get a pretty good idea what she likes.  Even if I'm the one in control I simply ask her to guide me into how she likes it.  No woman is exactly the same.  However, most women I know love to start out with light, barely touching the clit, licking before progressing into more aggressive licking and sucking.