The best way is to interact!

We may not have been a very close class in school, but there's no reason we can't be now.  People change!  You would be surprised to find out that the classmate you didn't care for at all in school, has grown into a wonderful person that is a pleasure to know today.  I have found that to be true, time and again.

People like to be noticed and remembered, so don't be shy;  let them know you remember them and maybe even tell them that you always wondered what happened to them. Leave a comment on their profile so they know you were there, even if it's just a quick hello.

Reach out and say hello to a classmate you've never spoken to before!  Get to know each other & maybe make a new friend.  You can never have too many friends. 

Did you know you can upload all the pictures you want on your profile?  We'd love to see pics of your families, vacations,  your dog or cat; whatever you'd like to share.  

Haven't shared much or anything at all on your profile? The more info you add to your profile, the better we can get to know you.  Whether you've led a quiet, uneventful life or an exciting one, it's all interesting to me and I'm sure it is to others too.  I love reading the profiles! 

Make sure you take advantage of the Private Message option!  Under every member's master photo you will see a link to send a private message to that person.  When you use it, the system immediately sends an email to that person, letting them know they have a private message.  This is the fastest way to reach each other! 
If you only comment on their profile, they may or may not get notified that someone left a comment, so they might not see your comment until they come back to the site; in some cases, that could be days.  It all depends on how they set up their notifications.