This is kind of an odd question, because the answer is literally every single other conceivable job. I mean, whatever you like and whoever will employ you…? Playing in the NBA is a good alternative to any job you can’t get if you can play in the NBA. So is captain of a cruise ship. Or restauranteur.
I guess the main advice is to not plan on a career creating languages. I’m pretty much the only one that’s ever had that career, and it could dry up any second (just learned today that a new show I was hired for has been canceled before it even started filming). I never planned on having this career, and it would have been irresponsible of me to expect that conlanging could have turned into a career at pretty much any time in my life before 2011.
My original plan was to teach, and that’s what I did. After I got my master’s in linguistics I taught as an adjunct faculty member at Fullerton College. I’ve always been passionate about education, and I imagine I will return to it one day. Education is something I’ve always been around and always wanted to be around, but it also afforded me time to write and create languages and do what I do. It was an ideal field for me.
So the question, then, actually doesn’t have anything to do with conlanging specifically. The question is what do you want to do? What are you passionate about? Then, how do the answers to those question intersect with paid work? Conlanging is just an art, so if you step back and look at it as that—as an art like writing, painting, animation, etc.—then the question is what can you do to earn money while giving you enough time to pursue your art? This, I’m sure, is a question that has been answered many times in relation to the other arts—especially writing. If you look for advice given to aspiring writers, I’m sure it will apply just as well to aspiring conlangers.
In general, though, if you’re looking at staying in the same place for a while, I’d try to find a job that could lead somewhere. For example, you can make a lot of money as a waiter or bartender, but these jobs don’t lead anywhere beyond what they are. They’ll always be there, and you can always pick right up anywhere new, but there’s little room for upward mobility. If you could get in somewhere where there is the possibility of upward mobility while still getting enough time to pursue your art, that’s ideal, because then you’ll have something with a future while you’re waiting for your art to come through.
Of course, I’m also not a great person to give career advice. I went to graduate school because I didn’t know what I wanted to do, and then immediately went into teaching at a community college—and from there to Game of Thrones. Before that my only non-school job (e.g. being a TA at UCSD, working at the Northern Regional Library Facility while at Berkeley) was at a Togo’s (a sandwich shop). I didn’t last there long. I was extremely fortunate to have the financial support I did while I was going to school. Not everyone has that—and those that haven’t have much more inspiring stories, and, in my experience, give much better career advice. I encourage you to seek them out.
But, of course, in the meantime keep conlanging. That’s how you get better at conlanging! :)