There's all manner of factors which go into it. I just finished a season with Chelmsford in the National League South. It was my first full season, having started the game unemployed. We overperformed expectations - Finished 4th in the league but lost the playoffs (expected mid-table finish), got to the 3rd round of the FA Cup and the semi-final of the FA Trophy.
At the end of the season, I had job offers from 4 League Two clubs and one in the Scottish Championship. I put that partially down to the overperformance, and partly down to Chelmsford allowing me to take coaching badges (at the time I left for Forest Green, I was studying for either a Continential B or C, can't remember which).