Sometimes a painting doesn't work out no matter how hard you try; I recently had this happen to me for a watercolor commission that I just finished. I was working on the first version of the watercolor and I was almost done... But then I looked at it and immediately knew it wasn't good. I've had this happen many many times, but it's always important to realize when you should fish and when you should cut bait!
1. As yourself: How far along am I? Is it almost finished? If you're almost finished, then there might not be much hope, but don't give up too easily. If you just started, then keep working and see how you feel when you push through the difficulties.
2. As yourself: Do I feel like I could do better if I redo it? This is a tricky question because I honestly feel like I could always do better, but the point of this question is to realize when you can do better and when you should just be satisfied with what you have.
3. Show the artwork to your friends and family. This is a tip that I learned really from reading the autobiography of the artist Norman Rockwell. Rockwell used to show his paintings to everyone to get opinions...even his mailman!
4. Sleep on it! I don't literally mean sleep on your artwork, but I mean get a good night's sleep and look at it again in the morning. Sometimes you'll feel better the next day and you'll have a better perspective when you leave it be.
5. Never be afraid to redo something. I know that sometimes a painting or drawing can feel like it took years to do (and sometimes they actually do!). But it's important to remember that it's never too late to do it over again. Stay strong and keep drawing and painting!
If you find yourself unhappy with your artwork, here are some questions to ask yourself and some tips that I hope you'll find useful: