If you want to do a thing, do it now, or as soon as feasible. Because there might not be a later.
If it is a complicated or expensive or hard thing that takes many stages or has a steep learning curve, start working on the parts you can work on while you can work on them, then move on to the next thing. Accept that there will be a lot of failures along the way, and that you can come back from nearly any mistake that doesn't involve making a left turn in front of an oncoming semi. Concentrate on yourself and what you can do, and don't rely on other people to fix things for you, even though you might love them or they you. (This doesn't mean you can't love friends or family or partners. Friends and family and partners, in the long run, are the thing other than Useful Work and Adventures that make life worthwhile. Well, all that, and a really nice coffee and tea kit in the kitchen and the skill to use it. But that last thing isn't terribly expensive unless you make it be.)
But to succeed at a thing--a job, a relationship--in the long term, the thing is: You Must Commit, even though commitment is scary. And commitment is scary because once you're in you're in. It's not bobbing around close to the shore, paddling with your feet. It's both feet and swimming as hard as you can out where the rip currents and the sharks are, where the water turns blue.
You can't hold back because you're afraid of getting hurt: you have to accept that you are going to get hurt, and put your hand in the fire of your own free will.
It's like climbing. You can make sure you've got good ropes and a belayer you trust (you SHOULD make sure you have good ropes and a belayer you trust!), but there's moves you can't make unless you're willing to risk falling. I'm not saying follow your bliss off a cliff, in other words: part of being prepared and committed is having the right kit, whether it's money in the bank for the lean times when starting off as a freelancer, or a partner who supports your work, or being young enough that starving in a cold room for a few years with pneumonia is romantic (I have the T-shirt!).
That's why it's scary. It's scary because you are taking an actual chance.
But: things don't work out the way you want them to if you just kind of drift along seeing what will happen. Nice things might happen! ...but they didn't, for me.
Basically, what I figured out was that I had to be a protagonist if I wanted anything to happen, and part of being a protagonist was accepting that I might fail. And then have to deal with that failure. And that if I didn't do it I would more or less inevitably fail, but I could pretend to myself that it wasn't because I wasn't good enough and that I didn't know why.
Seeking success, in other words, meant letting go of a layer of ego defense.
This realization directly led to me having the career I always wanted, and doing pretty well at it.
It also led to me having the best relationship of my life. I wish I'd learned it when I was sixteen, rather than twenty-nine, but I had some things I had to work through first.
So that thing you want to do? Assuming it’s not illegal or immediately fatal? Do it now.