In part I of this post I've started dealing with the problems that stand in writers' way to completing their novel. Here I'm going to continue.
2) A novel - that's long isn't it? Well, yeah. But no worries, it's not so much. Don't forget - many writers do this everyday. You can too. Here's how. Divide your work, give yourself a schedule. If you have an outline, combine the schedule with the outline, but if not, just decide on how many pages/words you want to write a day. So let's say the average novel nowadays is about 100,000 words. If you can write 1000 words a day, about 3-4 pages, then you will have completed your novel within 100 days (about 5 months if you don't count weekends). That's doesn't sound so bad now, does it?
3) You get stuck. Usually the reason writers get stuck is because they don't know the ending. If you know the ending, you have what to strive for, even if you don't have an outline. So always know the ending.
4) You think what you've written so far sucks. You may or may not be right, I can't tell you. However, what I can tell you is that unless you write, you won't improve. And no better practice than finishing your novel.
5) Maybe this new idea you have is better. Maybe not. But you must finish this one first. If you're afraid you'll forget the new idea, write it down in a notebook, you can always write another novel after you've finished this one, and the more ideas, the easier it will be to start the next one, but if you continued to jump from one idea to the next, you'll never finish you novel.