To keep it simple I'd find a pleasant local route that takes you about about 30 minutes to complete (with few if any reasons to stop, or coast, along the route).
Then I'd get a HRM and Strava, and link them. Create a personal Strava segment for the 30 minute route.
Then, once, or twice, a week (max), I'd Time-Trial it as fast as I could.
Get home and log the Strava data:
Time for segment
Average Heart Rate
Estimated Power (Strava is pretty good at this).
Strava will show you a graph over time against your segment so you don't need to do much.
If you are honest about it, and really push hard, I'm confident you'll see rapid improvements, whether that's in reduced times or reduced heart-rates for the same times (which is actually very useful for fast touring).
Alternatively go out for an hour and plot three or four 5 Minute segments along the route and go "balls out" in each of those segments. Either way, there's usually more gain to be had from short, intense, efforts than plodding around for hours without a plan.