I've been trying to write something for years but I can never seem to commit to one idea. Any tips for sticking to one project?

Hello Nonny!

So, managing one idea is something that people have asked me quite a few times in the past, and I like to give the same answer each time: you don’t have to. Having two, three - (or more) - projects on the go at once is a great way to keep your productivity and creativity flowing.

If however you want to stick to one exclusive project, then I would reccomend a few things

Digital savings - keep a file on word, google docs, evernote or whatever else you like to use and save all of your ideas. You can add to them when the inspiration comes back, but they’re only notes. This allows you to continue with one main project while not losing sight of the ones that you also have inspiration for.
Change your focus - are you trying to write full-length novels or novellas? Then perhaps you’ll find that short stories are the way that you want to go. Authors like Niel Gaiman churn out books of short stories and enjoy just as much success as more traditional novellists.
Dip a toe in first - there isn’t any pressure to launch in and write a full book or anthology of short stories straight off the bat. You might find it helpful to go back and focus on the basics first, rather than putting everything into one project. Find workshops, chat with fellow writers, submit stories to magazines and enter writing competetions. Get a feel for the market and the community, and take your mind off that One Idea for a while.
Sharing - Try putting some of your ideas on a site like Wattpad, and see how they are accepted. Having feedback and finding people to bounce ideas off of is incredibly useful.
Merging - Can you combine any of your ideas? Take the elements that you like best from each one and mash them together. You have draft after draft to figure out all of the kinks and see what works and what doesn’t. It’s trial and error, with no consequences for the error.
Patience - This last is often the hardest to accept, but it’s true. You do have to be patient. The ability to stick with just one or two ideas is something that comes only as you mature as a writer. I’ve been writing for almost eleven years and still, I’ve only just begun to develop the patience, maturity and dedication needed to stick with a project.

Thinking about maturing: you’re likely to hit a turning point or a learning curve, but it’s so important that you don’t stop writing just because you can’t stick to one thing, and never get rid of your old projects. I said that I’ve only learned how to settle down on one idea recently, and by that I mean early 2017/end of 2016. I realised that the way that I had been working my entire life wasn’t right for me, scrapped all of my ideas (but didn’t get rid of them. They’re in a box) and started again.

Everyone’s process is different however, and what worked for me may not work for you. Although I can advise you of different steps that you can take to grow as a writer, a lot of the discovery is up to you. On writeblr alone there are hundreds upon thousands of resources and advice blogs like myself willing to help, and I’d bet you my last packet of Walkers that almost all of them have been (or still are) in the same position that you’re in now.

Good luck! I hope that at least something here will be helpful for you ^^