The point is this: try not to involve yourself into something so completely that you send off ' I'm busy' vibes.
You want to seem approachable, and hiding behind a laptop or book doesn't help!
Coffee shops are one of my personal favorites when it comes to places to meet singles.
It may seem obvious to some or completely alien to others - yet it works.
Separate from the obvious, there are several social events you can attend to increase your chances of meeting someone new.
Try planning a weekly movie night through your friends and see who shows up every week, making it clear that new people are welcome to join at any time.
These are both valid points, but neither are reasons to not try out some of these places to meet singles on your own.
Perhaps a change of venue or attitude will make all the difference, but without trying you'll never know.
Bus stops, laundromats, libraries, restaurants, bookstores, grocery stores and travel-related places (buses, trains, planes, etc.) all fall within the public place moniker, although there are surely many more to choose from depending on your specific lifestyle.
For those in smaller communities where the resources may not be as comprehensive, try talking to the owners of local shops you frequent to buy hobby-related materials and ask if they know of others to speak with regarding starting a group, or if you can post notices looking for other interested participants.
Another idea would be to contact national organizations overseeing smaller local chapters to see if they are planning any speaking engagements or are looking to start a chapter in your area.
Find a busy coffee shop that you feel comfortable in, and take up a space near the main door.
Avoid bringing anything to distract yourself with if you can manage it, although this may be more difficult for some than for others.