For my role players I usually invest in either 1 key talent necessary for their position or awareness if they are low every week as the points become available. For my top 10% I will save until I can bump their consistency or give them the high motor trait if they dont have it. For rookies or 1st year players that were taken in rounds 1 or 2 I'll save and give them the 50k upgrade to make the most out of it.
I also make sure to invest my coach xp in positional xp boots for any position where I have alot of rookies. I am playing the Bengals so my first investment was in the WR xp boost so that I could get AJ to elite status and speed up Sanu and Jone's development.