Yes, smile, unless you're unfortunate enough to have a gate agent who is rude to you and determined to make you feel like scum for even approaching her (was female & possibly the same person, both times this happened), in which case the best you can hope for is to restrain yourself from punching her.

I must stress that this is not the norm! Most of the time the KLM gate agents at AMS are great, even if no op-ups are available.

I didn't know about tip #2 because normally we go through the gates as soon as possible, so thanks for that! ^