Still using the Nikon D5100.

This is no doubt not an issue with the camera and more likely a case of me being a complete dummy when it comes to cameras and not knowing settings or anything that work best when photographing in this hobby but... I just can't seem to achieve the quality of photos that I probably should be.

The biggest struggle is when I have to manually select what mode, shutter speeds etc the camera should be in, often the images are not coming out totally clear (usually blurry, not in focus or looking slightly distorted) another issue I always have is the photos either turning out far to bright or dark, recently had to take a photo of a Stagecoach Yorkshire StreetLite in Sheffield and I ended up taking something like 50 shots of the same bus and only managed 4 photos were the lighting was correct and the quality was right.

Anyone know where I am going wrong?

I am maybe looking into possibilities of upgrading but considering how expensive cameras are, I'm unsure if it is worth it, especially if I end up making the same mistakes that I seem to be making currently.