- editing as you go. i.e. pausing every twenty pages or so and looking for typos and inconsistencies.
- editing once the rough draft is fully done
For Seat of the Pants writers like me, editing once the manuscript is complete may seem more reasonable. We tend to write as the inspiration hits us, and we don't like stopping in the middle of a scene to go back and look for errors. But Seat of the Pants writers also have a very hard time writing good plots. If you write when the inspiration hits you, try some self discipline and edit as you go, it may be easier to correct plot problems.
For Plotters (writers who spend much of their time planning incredible, layered plots, with well developed characters) editing once you finish a manuscript may be easier, especially if the writing of the story doesn't come as easily to you.
So persevere in the editing process! Both ways can prove difficult. It's hard to take a knife to your creation. And don't be afraid to find someone who you can critique with - someone who really knows what to look for and what editors will look for. My critique partner, Esther, is simply amazing at finding the flaws in my work. It hurts at first, but their advice can be extremely helpful if you take it.