This is what I can see, it's difficult at these image sizes to pick out every aspect as I can't see detail but here goes...
No. 1. There's no aperture recorded but I'd imagine it's pretty wide as your shutter speed is over 1/3000 even if at ISO 50. It's hard to tell about focus etc at this size but one obvious thing is that some of the highlights are blown.
No. 2. The shutter speed here seems to be 1/10. Even with the camera mounted on a tripod I think you're probably going to get some subject movement if there's even the slightest breeze.
No. 3. 1/60 with blown highlights.
No. 4. 1/40 @f9 and 78mm.
Here's a few basic things I'd suggest.
1. I'd forget about ISO 50 unless you are making a conscious decision to use it, perhaps to get a very low shutter speed.
Try and use the lowest ISO that you can but don't be affraid to raise your ISO if required. Keep an eye on both the aperture setting and the shutter speed and raise the ISO if you need to to get a good balance between the settings.
2. Unless you are using a tripod or image stabilisation try and keep the shutter speed reasonable. It's difficult to be exact but I'd recommend you try and keep your shutter speed faster than your focal length. For example if you are shooting at 70mm (one of your shots seems to have been taken at 78mm) try and keep your shutter speed above 1/70 second and in fact I'd be much happier at 1/150 or faster.
3. Try and avoid extreme aperture settings unless making a conscious decision to select them. Read up on Depth of Field and study some depth of field tables.
Google and you shall find.
4. Exposure. Exposure is a mix of ISO, aperture and shutter speed. I think that it might be an idea to select evaluative metering unless making a conscious decision to select something else such as centre weighted or spot. Keep in mind that your camera may not be able to capture the whole dynamic range in some scenes such as a relatively dark foreground and a bright background. In some shots when the centrepiece of the shot is for example, your stag, the sky in the background may blow. You can overcome this by metering for the sky (using a faster shutter speed) but this will give you a darker stag. So, you may have to get a balance between the stag and sky if you want to retain both. You could meter for the sky and then boost the fill light in post capture processing to brighten a dark stag and this really isn't that difficult.
5. PLAY!
As shooting digital images is basicaly FREE
I think you should go out and shoot lots of pictures with different settings and see what the results are and what the effect of changing different settings is.
Personally I normally use Aperture priority or Manual. I select what I think is an appropriate aperture and I balance it against ISO (trying to keep it low) and shutter speed (trying to keep it quite a bit above focal length.) Until you get the hang of things you could use f8 and ISO 100 as starting points. If the shutter speed looks too low raise the ISO to maybe something like 400 and if that doesn't bring the shutter speed up high enough use a wider aperture and see how the shot turns out.
Actually, I should mention focus. I use centre point only but I also zone and hyperfocal focus. Until you get to grips with everything I think you should start with centre spot and focus on the main thing in your picture.
Sorry to go on at such lengths and I'm sorry if I've covered things you already know. I hope I've helped a little and if you need any more help or advice please just ask and I'm sure someone will be here for you
and at leaast your composition seems ok, they all look like good pictures and it looks like you have an eye for a good picture so... I hope that you can soon get to the point that you can capture an image that you're happy with
