1) Don't pick your career by subject area - pick it by the skills you enjoy putting to use. 'Ukulele' is not a skill or action, it's a noun. Being a ukulele salesperson or a ukulele craftsman are two very different careers. What are the specific skills you want to spend most of your life exercising? Again, focus on the verbs not the nouns. Pick a career that allows you to do what you do best every single day.
2) Be very wary of tournament professions. Tournament professions are jobs where 10,000 people compete for only one spot. The person at the top makes a million, and everyone else starves. Acting is a tournament profession. Writing fiction is a tournament profession. Being an olympic athlete is a tournament profession. And, yes, ukulele playing is a tournment profession. If you embark down this road, make sure you have either amazing talent, rich parents, or an incredibly thick skin for suffering and angst. (And preferably all three.) The weird thing about these professions is that everyone looks at the top of the pyramid and somehow just ignores all the many many people who failed trying to march to the top.
3) Be decisive. The most 'successfull' people I know are not the smartest people I know but the most decisive: they made a decision and stuck with it. I've been a little shocked at the type of success someone can produce from true dedication, stamina and focus over many years.
4) Imagine yourself as a mediocrity. (Really!) Too many people imagine themselves as super successfull when they choose a career. There is a whole generation of lawyers who choose their career while watching LA Law who now spend their entire professional lives reading mind numbing contracts and wills all day long and they hate what they do. When you imagine yourself as a crazy success every career seems amazing. But only some careers still sound cool if your'e just ok at it. If your career choice still sounds ok even without tremendous success, that's a good hint that it's a good choice for you. (In other words, that's a sign you enjoy the profession as an end in itself and not just as a means to something else like money or fame.)
Yes, far more than what you asked for... my apologies.