Spreggy

I think that in a nutshell you need to pick a plan and stick to it. At your current level, and half decent plan will yield big results. Here's one I am about to start for the winter workout:
https://www.saris.com/p-364-realrides...ining-dvd.aspx

Here are some more:
Online:
https://www.freetrainingplan.com/

Good book for where your level is, has three progressive plans, based on testing where you are now:
https://www.amazon.com/Lance-Armstron...=1H24WVRAOUNYH