It's not buying some new tool.
It's not taking a class.
It's not making a template.
It's not even using a plastic bag (although that's a close second).
The easiest thing you can do to improve your spoon carving is to choose better wood.
This sounds obvious, but how many times have you picked up a bit of wood, started working on it, recognized a potential fatal flaw or major issue, and continued working on it anyway? (Everyone's hand is in the air here, including mine).
Wood that has a poorly placed knot. Wood that is too spalted. Wood that is too twisty, wood that has grain tear-out, wood that is too short, wood that is a hard species or is hard because it is too dry.
Why do we do this to ourselves? Somehow we have a culture where it is considered cool to keep going in those moments when really, I think, it should be cool to throw it out, put down the knives and go spend more time getting better wood.
Maybe you need to search more. Maybe you need to cut down a tree. Maybe you need to befriend an arborist. Maybe you flat out need to buy it. But better wood will always pay you back many fold for the effort of getting it. And you can do that no, immediately. You don't need to earn the skill of having better quality wood. You just need to recognize that it is worth your time and perhaps money to procure some.
If you can, curate a selection of wood, because if you are aging it in the log, they will be best at different times depending on the diameter and length and when they were cut. Keep it outside, in the shade if possible, in as long a length as you can handle. If you are buying wood from someone, try to make sure they are someone with access to a whole lot so you aren't getting their dregs. Keep it wrapped in plastic in the freezer.
This is the easiest thing you can do to improve your game. You can do it now. You can invest the time without needing more skill. But it will magically feel like all of a sudden you got a lot more skilled.
My blog has evolved into a series of short essays on the nature of entrepreneurship, craftsmanship, and their overlap. If either of these topics is something you think about, you will probably like this.