The first thing that you need to do is psyche yourself up. What was once a hush-hush activitiy is now an accepted way of meeting people. So turn on your computer and find the site that is ready for you.
There are a ton of sites geared specifically at matching up like-minded Jews. Do a search and keep in mind that different sites have different types of Jewish people. Look for a site that seems to contain people from the demographic and religious or affiliated level you are looking for.
Next, create a profile. Don't sell yourself short! Make it witty, make it cute, but above all make it represent who you really are. Definitely upload a photo, as searchers often perform searches only for profiles with photos. Now you can either search from some available bachelors or bachelorettes that spark your interest and strike up a conversation, or you can sit back and relax and wait to be contacted.
One thing to keep in mind: don't keep the relationship 'on-line' too long, or illusions will start to build. Meet up early on in the relationship, but just for coffee so as not to get stuck in a long meal with someone way off. And remember, above all this is a number game. The more people you meet, the more likely you are to meet someone of interest.
And one final tip: Once you have met, don't chat online, even feel free to 'block' the person on your buddy list - at least for the beginning. It's better to let the relationship progress more naturally where you can gage the person's interest by how much time is spent on the phone or in person, as opposed to how often you 'bump' into each other online. Let nature take it's course and, above all, have fun!