You have to start a manuscript to finish one. And, as I've said before, finishing a first rough draft is how I begin to really see the structure of my novel and understand what it's about. But before that I have to stumble through rough territory. A lot of that first draft my characters are the walking dead, but I keep pounding away on the keyboard and trying to give them life. A lot of the story is clumsy as a drunk trying to walk a straight line but... And the language--painful to look at in places. BUT there are moments of joy and enjoyment in all this and some good writing, too.
You have to get through that first draft though. Enjoy the discovery moments and force yourself to write even if you know it's not that good. You have to finish that first draft to have a second and third. Not all of you will work this way but many of you will; I do. You can go back while you're writing the first draft and improve sections and tinker with ideas and plot and make that first draft a little better. I do. BUT don't allow yourself to do this INSTEAD of pushing on. Your goal each day should be to push on and move the story and characters forward so that you can get to the moment where you type THE END. Keep thinking about making connections in the work to help you keep it on track but know that you will wander off sometimes.
I think there is nothing more important for an inexperienced writer than finishing work. Know that the first few months of writing something new are maybe the toughest because the writing is so rough and you're discovering your way. Force yourself through it.
Allow yourself to write badly in order that you may write better.