Obviously, the most important part of writing is actually doing it, and it doesn't matter if you have the best idea in the world it will never amount to much if you don't sit yourself down and write it out. Every writer understands how difficult it can be to force yourself to work on a project that seems endless, especially if you're novel has been going on for months or even years with little signs of progress, but the golden rule here to remember is that if no attempt is made, nothing gets done.
Also, don't be afraid of butchering your good idea. A lot of writers are afraid that if they try to write down their good idea and find that their skills are somehow inadequate, they'll find that they didn't believe their idea to be so good in the first place. However, the whole problem with writing is that you seek to express that which can't be explained in mere words. The trick here is to simply not lose sight of the original idea. If you begin to confuse your poor piece of writing with the great idea you originally had, you'll throw them both out without giving that idea a chance to shine.
Finally, don't worry about what other people think. Eventually you're going to feel the need to present your work to somebody else, since the whole point of art of any kind is to express to others ideas that are important to you. Remember, however, that you're not writing solely for the purpose of pleasing othersyou are writing for yourself. So if your best friend picks up a manuscript that you think is a smash hit and begins to humor you with comments such as "interesting" or "this is awfully long, isn't it?" the way best friends sometimes do, don't let it get to you. However, do not close yourself off entirely to their advice, if they have any to offer. You must strike a balance between writing something for yourself and writing it to be understood by othersif others don't understand it the way you meant for them to, you might have to change something.