Having only written fairly short stories during my teenage years, I hadn't really worked out a method when I first started on my current novel. I settled for writing a synopsis of the plot at first. But as I began to write, I realised that I often forget what colour eyes a character has or old they're supposed to be. So I have now also written character descriptions for all of my main characters. I am hoping that this will limit continuity errors.
For a few settings, I have been able to find photographs on the internet, immensely helpful when writing physical descriptions and trying to imagine how a place might make a character feel. But, obviously, some places are complete fabrications of my imagination so I have also written notes on physical features of certain settings, such as the main character's home.
I have made the perhaps silly decision to write in first person, present tense. So often, when I check back through my writing, I find that I have accidentally used past tense instead. Hopefully these little mistakes will become rarer as I write more.
Every time I open the file to start writing, I read back over what I have already to try and get back into the correct mindset. However, while doing that, I find things that don't sound quite right or that could be improved. I end up doing at least ten minutes of editing before I even start anything new. I have no idea if this is normal. I hope that doing my creative writing course later this year will give me better insight into editing techniques. For now, I shall continue this way.
I also have the problem of getting a little distracted from writing. For instance, this very post is being written when I had meant to be working on the novel. Email and Twitter are other common distractions when I get even slightly stuck. I have no solution to this. Instead, I give in. It does mean that when I get around to actually writing, my mind is a little clearer.
I would be interested to hear how other writers overcome these problems or plan out their work.