I do a fair amount of practical tests for pilots on an accelerated training track. Someone asked me recently about the "perfect" way to train a pilot in a theoretical world in which there were no cost or time constraints.
In my mind it would be fairly simple -- fly at least one hundred hours (100-200 would be the truly useful range, but 100 minimum) utilizing the certificate or rating just achieved before moving on.
In my subjective view there is no more valuable time to learn and grow as a pilot than directly after earning a private pilot certificate. In my vision of how best to build a complete and well-rounded pilot, the assignment would be for that pilot to fly VFR across the country (maybe even some light international travel towards the end of the time) dealing with all the usual challenges faced by VFR-only pilots. Weather, mechanical issues, challenging airspace, having to make an unexpected stop and wait out a frontal system, and so on. Back in the day that would have (and did) include stopping at a flight service station, doing a tour of a tower cab, spending a day or two shadowing a mechanic performing an annual or 100-hour inspection, etc. All of the little details which gives context and understanding to the knowledge and skills recently gained.
The same assignment would take place after earning the instrument rating. File and go -- based on personal minimums which are carefully but continuously reduced to a level at which the instrument rating is a highly useful tool. Seek out safe ways to increase the comfort factor with weather which was once considered dangerously challenging, but can be whittled down to a manageable bite-sized chunk with exposure. Get a few tune-up flights with instructors during this time to correct any bad habits creeping in.
Of course, in the real world, this could take years to accomplish. In the modern professional pilot training track these are luxuries which are simply unaffordable for most.
For part-time, GA pilots, it is possible, though... if you're not on a timetable to complete training, take advantage of the time you do have to flesh out the skills you've most recently learned before moving on.