Wildlife with M (240)?
It's probably not the idea camera for this, but I had a go. My experiences are:
1. Pick your lens carefully. I tried a modern Nikon zoom telephoto (via a Novoflex adaptor), but it was hard to focus (high gearing on the focus ring) and had ineffective aperture control. Plus fairly severe vignetting. So I went for a second hand Nikon 180mm manual focus lens. Much better as it's actually designed to be used in a way that broadly fits the M (i.e. manual control). Plus, it doesn't vignette. But it seems to be incompatible with my Nikon teleconverter, so it's a bit less flexible.
2. Get one of the handgrips. I find it really hard to hold the camera with a big lens on without this.
3. Get the accessory viewfinder. Focusing is very tricky with a long lens. The way that the viewfinder adjusts the brightness automatically is very helpful, particularly if you stop the lens down a bit.
4. Use the zoom function in the viewfinder for critical focus.
5. Have a stationary subject! It takes too long to get the focus right unless both you and the subject aren't moving.
With all that, I got some acceptable results, to me anyway. One example posted below. I'm not claiming this is a great photo and you can see that the plane of focus is a bit behind the eyes. Note also that this is a crop, but I find that this lens works ok out to the corners. It's a crop because the DPReview website objects to the size of the full frame pictures I've got for some reason that isn't clear (I don't think that they break the size limits). If you think it's not quite sharp, I'd like to point out that it was also handheld.
|_F0A5334-Edit_small by Dester Wallaboo|
from Open Air Fashion Photography
|Feed me, me, me, me, me by Denjw|
from Attention-Seekers in Nature