Clipping back in was the biggest issue for me when I started out. Failed clip ins would cause me to get stuck at a light until the next green light. I found that if your first push isn't enough to get your foot clipped in, pedal a few times with just one foot to build momentum. Or (I use SPD-SL's) I just place the unclipped foot ontop of the pedal regardless of the side and pedal unclipped. But don't do it for long because the foot can easily slip off.