In this height of the sun spot cycle, I am often called by QRP stations. My ears are often strained much to copy them. The following items are already well known technique for QRPer but, hopefully, should be confirmed again by them.
First, QRPer should not add /QRP etc after their call except for in really good condition when QRP signal are supposed to come through loud enough. "/QRP" is often mixed up with the call itself. Imagine how much I feel disappointed to hear "/QRP" on the plateau of the fading only when I could copy it. "/QRP" is not the licence to avoid the toll. It is of much less important thing for the receiver than the call itself. Too many QRPers are reapeating "/QRP" and eventually mixing up the receivers.
QRPers should be most experienced operators. They should know how the bands open. They should do with the phase of fading. In noisy conditions and/or long phase fading, they should slow down the speed of keying irrespective of the other's speed. Of course, they should make least mistakes in sending if not perfect. They should send the message in most compact way. No too abundant messages. It is always impressive to hear how an experienced QRPer sends the message rationally. I learn from those operatros much.
In summary, QRPers should be most imaginative for how his signal is received at the other side. He should train himself to achieve excellent operation technique as well. Yes, QRPers must be the best operator among all hams, I believe. I am thrilled and pleased to see such a QRPer on the air.