Thought I should write up something just to let everyone know I'm still floating around dA. Lately I've been getting some watercolour practice in whenever I can. Currently working on one in the mean time! Unfortunately, sometimes I have days/nights where I can't stand or figure out what's wrong with it. Maybe it's just me? (Most likely D: *gasps*)
Most artists that I know or read their articles/blogs do suggest taking a break from the project, look from a further distance or even just close your eyes for a timed moment. I agree that taking a break from a project is good and lets you relax a little, but we can't mix this up with leaving the project to when we feel like getting back to it! Then you'll just feel sluggish and let it collect dust. My breaks usually consist of taking a walk down the hall of my house, get a drink of water, check fridge or even see what's happening in the lounge room. This helps get my mind off of the project for a short while and refresh it with a new environment. But a big help would be moving back a fair distance from your work. The human eye can eventually trick you the longer you work on something, which in turn could lead to not seeing what you want, which leads to frustration (in my case). But by looking from a further distance your eyes don't have to pick up too much information and most times your work actually looks awesome and is coming along. This works well if there are a lot of blended components in the project, which leads to Impressionist Painting (apologises if I'm wrong ><")
So the main point here is to always take a short break and give yourself a little distance from time to time from the project.