I recently bought a manual lens on ebay. I saw some pictures taken with a manual lens on flickr and got curious. Some minutes and EUR 88,- later (USD 125,-) I was the owner of a Revuenon 55mm f1.4, an adapter for the M42 screw mount to EF and a lens hood.
The first impression was heavy. This glass is built like a tank. Metal everywhere. Great! And the aperture is 1.4 so it is fast. The DOF is shallow. So the first tests were on how the glass reacts to bad lighting and how to operate the little gem.
So the first thing I learned: Take your time.
In some light conditions it is fairly easy to focus with the view finder, but especially if you are close to the object it is better to us the liveview. The DOF is so shallow that it can be the trickiest part of the whole procedure to focus.
Once I knew the signature of my glass I took it for a walk. And I had fun!
Feet of steel will show you, that the DOF is shallow! Recognize the small strip of sharpness on the ground. Small details like this can be useful when focusing by hand.