State your purpose
Make it clear why you are on the site.  You need to make sure people know you are there for business and not for finding a relationship.  This is important or else you will be bombarded with offers from the opposite sex to chat and get to know each other which can be a he time waster.

Follow the rules
Make sure you know and follow all the rules.  These sites can be strict and if you break the rules you can get banned.

Keep it updated
Visit your page often.  Everyday would be ideal so that you can keep everything up to date.  Plus it shows up that you are visiting the site and so people will know you are an active member.

Use photos
Have your photo on there.  It has been shown that pages with photos get more traffic and interest than those without photos.

Try social media sharing sites
Try out sights where you can share your stuff.  These sights are like the social networking sites, but they actually let you submit things like photos and writing to them that remain on their network and are shown off to visitors.

Customize
Customize your page to fit you.  Add in backgrounds and other fun stuff to show off your personality.  Remember these sites are for networking and getting to know others.  People want to meet a friendly and fun person so be that.