Depends on the level of involvement from the opposite sex, look for indicators of eye contact or interest before approaching to make a complement. Don't use too many complements as this will be seen as flattery and the complements will become insincere and lose effectiveness but using a complement as an ice breaker is a great way to start a conversation.
I particularly like asking someone about their accent if I have heard them speak because you can open up a conversation asking them about where they are from and it can lead to the topic of culture.
Try to focus on more open ended questions as well so instead of saying "What do you do?" say "how's work?" and respond with "it's really good to see someone who enjoys to be valued for their creativity in a certain area" or "that's really interesting, what made you get into that?" and that can lead to a conversation. Avoid questions that will only lead to one word answers and this can be off putting and try to focus on being descriptive as possible but remember that a conversation is give and take.
Avoid asking question after question as this can be off putting and leads or a turn off, if the person only answers your questions with one word, back away from the conversation and if you want to leave the conversation, direct your eyes elsewhere and keep your body language turned away.
I suggest everyone checks out the CharismaCoach youtube channel which is great, he really explains communication in a simple manner.
[youtube]http://www.youtube.com/watch?v=EfIEyUTnS-g[/youtube]
Remember to make a concious effort to communicate and be as aware as possible, give someone your full attention when speaking with them and put in as much effort. Get out there and learn, join gyms, local groups, art classes, churches, sports clubs, singles events and other classes of interest. You should have a local paper or guide delivered or go to your local convenience store to ask for one, that should list the events that are on in your area.