Ollie's guide is a great place to start (the link Kijya posted). I'd also read up on some of the discussion follow his and TienJe's ghost guide, as they've both spurred some excellent conversations that flush out some of finer details of playing these kinds of 'sins (both guides are stickied). Also, if some of the technical details seem a bit daunting (claw and trap-laying speeds especially), check some of the other stickies at the top of the assassin forum page. Don't hesitate to post if you have a specific question about a particular part of the guide too.
That said, if this is your first assassin and one of your first PvP characters, you're going to be in for a rough time. I mean this in a positive sense, but there is a steep learning curve to this kind of character. It doesn't mean you can't get good with one, it's just going to take a lot of investment on your part. I've heard most people recommend starting out with a trapper if you want to duel with an assassin so you get the basics of namelocking, using mindblast to stun, and trapping in general. I myself had a few iterations of a kicker before trying a ww/trap hybrid and can attest they take a lot of practice to even get so-so with. However once you do you'll find yourself with a very solid 1v1 dueler (I'm not quite there yet).
Lastly, what realm are you on? It's probably possible to connect with someone from the forums on any realm that plays a ww/trapper. Give the player matchup forum in the community section a try. Best of luck with your 'sin. :wink: