This is really kind of the whole idea behind the "red, green, refactor" mantra. The point isn't to write perfect code right out of the gate, it's to write working code. Once the test is green, then you can refactor as necessary with the confidence that you aren't going to accidentally break things (as the test will backstop you).

Ironically, I think this is something that affects seasoned programmers more than new ones; the more you know about the trade, the more voices you have saying "no, that's wrong! Don't do that!", which can freeze progress. The way I combat it is by writing down pseudocode in my source code - literally just english, non-compiling pseudocode - which I then "refactor" into working code (thus the first "green" is "it parses"). By making step 0 the expression of the idea rather "writing the fist line of code", I can get right into the process rather than getting hung up on the "how".