This is where I admit I'm a procrastinator. Every time I get stuck on something my answer is avoidance. I hate to admit it but this sometimes actually works. I will walk away from something that I've been frustrated over, and come back later when my mind is clearer. This gets me back to work with a renewed sense of accomplishment. I wouldn't recommend this course of action though, it's just something I do if all else fails. I'll have to come up with something better if I have the opportunity to work under a deadline.
The issues that I get stuck on may be due to my lack of experience; for example, which tense to use and how to structure the storyline. I stop during writing to check the characters voice, or the plot line, then find out I'm not happy with how things are going. I hope in time this won't be such a problem, until then I have reference books on writing to turn to, and of course my critique buddies.
I could wish for a magic wand when I'm stuck. What's the purpose of struggling anyway? Then I noticed in the thesaurus that a synonym for struggle is strive, and realized that I'm constantly striving to make my story better, which is a good thing. I guess getting stuck is part of the natural process of writing, this struggle makes the end product that much better. I'll have to remember that next time I'm walking away from the keyboard and throwing my hands up in frustration.