Like Catrin said, there are many methods to mounting your bike. And there are some people will say are the "right" way. But if the way you do it works for you...

Personally, I could not be sitting in my saddle, clip in and geting going all at once. I straddle the top tube, clip in on the right (at the bottom of the pedal stroke) and then bring the right foot to the top of the pedal stroke position. I then push down with the right to get forward momentum and while standing on the pedal, bring my butt up over the saddle and sit down. Usually I pedal a bit with the right only before clipping in with the left, which gives me some momentum and thus time to get that left foot attached. To unclip, I first do the left, stand on the right, bring my butt up off the saddle and then bend my right knee until my left foot is on the ground and I'm straddling the top bar again.