It's party season. After that comes conference season, and then summer workshop season, then another conference season, and then party season again. At all these events, as well as many occasions in-between, you're going to meet, or spy across the room, someone you really want to talk to. Only you won't be quite sure how to start the conversation.
Starting a conversation with a stranger can be daunting, but it really isn't that hard. There are really only three rules: Be pleasant and upbeat; be open and straightforward; and say something the other person will want to hear.
With that in mind, here's are some conversation starters guaranteed to get things rolling. After that, it's up to you.

1. "What nice (or awful, or wet, or unseasonable) weather we're having!" 

There's a reason weather always tops the list of safe conversation topics. We all experience it, and we usually all feel the same way about it.

2. "Isn't this a lovely room?" 

If it isn't, it still might be a nice hotel, or a convenient or pretty part of town. The point is to comment--approvingly--on your surroundings. If it's an ugly room, you don't want to say so because a positive comment makes a better first impression than a negative one, and besides, for all you know the person's sister is responsible for the decor.

3. "Is this your first time at this event?"

If it is, and you're an old hand, you can offer to share information or make introductions. On the other hand, if the other person's been around a while and you're the newbie, he or she may show you around.

4. "I really liked that thing you said." 

If your target has given a presentation at the event, then picking something in it to praise is a surefire way to get that person's attention and good will.

5. "I really loved your last blog post."

If your target has published any writing online that you've read, say so, and mention something you particularly liked. (This works on me all the time.)

6. "That's a beautiful thing you're wearing."

It could be the other person's shoes, a piece of jewelry, or even a necktie. If you admire someone's taste, that person is almost guaranteed to like you. Commenting on someone's clothing or accessories is usually a better idea than commenting on his or her hair or other physical attributes.

7. "Do you know anything about the next session?"

If she does, she can tell you all about it. If they don't, you can speculate together.

8. "Do you know where the next session is?"

Most people love to give directions.

9. "Can I help you with that?" 

If the person you want to meet is struggling to juggle a briefcase, overcoat, and cocktail, for example, you can win points by offering your assistance.

10. "Are you having a good event?"

Asking what someone thinks of the event you're both at, and whether it's useful or informative, will almost always start an interesting conversation.

11. "Do you know what's happening next?"

What's going on in the next time slot? If the other person doesn't know either, you can figure it out together.

13. "What do you recommend?"

This could apply to a choice of sessions to attend, or hors d'oeuvres to taste, or even a tray of cocktails. Whatever the case, everyone loves to be asked for an opinion.

14. "I've been to your home town."

If you know where the other person is from, and you've been to that place or have any connection with it, that's almost always a good conversation starter. It can also work just to ask what the place is like, or what it is like to live there. (If the person comes from a large city, you can ask what neighborhood and go from there.)

15. "Do you know...?"

This is a similar conversational gambit to the home-town one. If you know someone who works in this person's company, or in the same industry, etc., it's great to inquire whether you might have a mutual connection.

16. "I've been wanting to meet you."

Sometimes the direct approach is best. Stick out your hand, state your name, and then tell people why you've been interested in meeting him or her. Of course, you're not going to say anything like, "I've been wanting to meet you because your company could really benefit from my services--let me tell you in detail about them."
As long as you're sensitive to the occasion, and to the other person's time, letting someone know you've been wanting to meet him or her in the hopes that you could do business together is perfectly fine. It might even increase curiosity about you.