Out of interest is yours a series 1 (FD) or Series 2 (GD) as 2012 was a transition year (edit: I'm guessing being December it's a GD) . So no problems with selecting 1st as well?
From my experience with 3 manual i30's we have owned the earliest one (2008 FD) was the notchiest. The late 2010 (MY11) FD and the 2014 (GD) were much smoother and easier to get into reverse and 1st.
There are threads on here about similar issues and from memory they talk about adjustment of linkages and or the clutch. You can also get an additive to add to the transmission fluid which will help shift quality. Some have even had their transmission oil replaced with a better one. I'm no mechanic though so let's see what others say...