I tend to be a reserved person, and I've noticed that many times when I approach somebody (not necessarily picking up women) I don't smile as much as I should.
When you have a serious expression on your face people tend to stay away. It tells the world you don't want to be bothered right now. Some people may even interpret it as arrogance.
We all know what an important non-verbal cue smiling is when dealing with other people. In fact it's vital for any type of social success.
However, if you're shy, nervous, or simply having a stressful, busy day, it may be difficult to crack a smile.
Of course, you could always fake it. I've tried this with varying degrees of success. It's better than nothing, but there is no substitute for the real thing.
So how do you crack a genuine smile when you really aren't feeling all that cheerful?
Simple: think of something hilarious when you make your approach.
I've tried this technique several times over the last few months. I always use it when I'm busy and stressed out over midterms or finals, and yes, IT WORKS.
Today, while dealing with a cute receptionist at my university, a Dave Chappelle joke came to mind, and I couldn't help but grin when I walked up to her desk. Flirting immediately ensued.
Had I not smiled, the dynamic of our exchange would have been completely different.