Thank you both for replying and sorry it has taken me a couple of days to respond.
I've tried some of the things you kindly suggested and will try more over the weekend.
I had already been experimenting with Aperture Priority mode since I got my 35mm f1.8 lens. I have also tried using single point AF mode since I noticed that most of my photos were a little out of focus.
I've found that even with the camera on a tripod and using single point AF mode, photographs (the single AF point specifically) are a little out of focus when using the viewfinder.
Again, when I take the same photo using the live view screen the focus is good. I don't understand why this should make such a difference.
I suppose the answer might be to always use LV mode, but that's not always practical.