Give him a compliment
Is he well dressed? Do you like his unique sense of style? Tell him! Everyone likes to be complimented, so telling him you like his cuff links or his choice of sweater is an easy way to open the door to conversation. Follow up by asking where he bought the item that caught your eye, where he shops or even whether or not he loves – or loathes – shopping. 
Ask for help
We're not saying be a damsel in distress, but depending on where you are, there are certain things you can ask for assistance with. For example, at the gym a no-brainer is to ask if you are using a machine correctly or tips for getting the most out of the free weights. 
Ask for an opinion
People like to offer their expertise and feel like they have something to offer. Whether you're asking what he thinks you should order off the sushi menu or what kind of organic coffee is best for brewing at home, no matter where you are, there is sure to be a topic you can get him to offer his thoughts on. 
Comment on a book or magazine he's reading
Take a peek at the cover of the book or magazine he has with him. Is it a book you love? One you've been meaning to read? Ask him about it, or, better yet, offer your opinion or thoughts on it. If his magazine is about a topic you're interested in (fitness, travel, pets) chances are, you will find lots to talk about if you mention of your similar interests. 
Bring up a current event
This means staying up to date with what's going on in the world. Read the paper, watch the news and stay current when it comes to politics and popular culture. If it's big news, chances are he's heard about it and there will be potential for discussion on the subject. Even something frivolous (Oscar nominations, Grammy winners) can be great fodder for conversation. 
Smile and say hello
The simplest way to break the ice is often with a nice smile. Once you make eye contact, give him a genuine smile and say hello. Then depending on where you are (party, gym, library) you can tailor any follow-up comments to your surroundings. 
Ask about his job
Sure, there are some people who hate talking about their jobs, but most people (whether they like or dislike their job) do like to talk about whatever it is they do. Just think about how many hours you log with your friends talking about work – the same penchant for discussing office politics applies to most people. 
Comment on your immediate surroundings
Are you waiting in line at Starbucks? Watching a terrible band play at a local bar? Make a comment on the situation that you share. You will immediately have something in common to discuss or complain about, making further conversation that much easier. 
Offer your opinion
Offer up your thoughts on something that can inspire conversation. At a bar, comment on the DJ. At the gym, tell him what you think of the new equipment. It doesn't have to be controversial, but use your powers of observation to hit on a topic you can say something about. 
Ask him to dance or buy him a drink
Be bold! Is there a cute guy standing alone at a party or at the bar? Take a deep breath, stand up straight, smile and approach him. Chances are, he will appreciate your confidence and respond favorably.