1. Spend some tiny amount of time building the simplest thing that represents your idea on an artboard. The focus here is to function as a first step, not to strive for perfection.
2. Identify one thing to change (shapes, colours, font, etc).
3. Duplicate the whole artboard, and tweak that one thing on the copy.
4. GOTO 2. Keep looking back at previous artboards and don't be afraid to revert if you notice that you've been off course for the past few iterations. Never delete an artboard, just go back and fork.
5. Stop when there's nothing immediately obvious to tweak.
It's a simple workflow that produces much better results than endlessly tweaking a single artboard, and you can see your evolution over time, so it's easier to identify the things that work / don't work to improve your skills the next time around.