For my planned PBP ride next year, one thing that I need to get right is making sure I'm fit enough. None of what follows is scientific, but based on my experience. I think it's better to have a plan and some targets to keep you motivated. This approach got me through my 1000km ride through Wales last summer, so I'm hoping it'll work again. The minimum training anyone has to do for PBP is the qualifying rides - 200, 300, 400 and 600km, which will be good training and practice for reducing faff, but I'd also like to improve my average speed so that I can go fast enough to get a bit more rest or perhaps make the ride more enjoyable by keeping a comfortable time buffer. Secondly, my last qualifier will be finished at the start of June, leaving nearly two months to lose fitness if I do nothing. My guess is that while experiencing at least one 600km ride is good experience, the training benefit of a 200km ride is probably similar. This is just a guess though, maybe there's something about the much longer distances which changes your metabolism or something. I haven't noticed it, though. The downside is that taking a weekend out for a really big ride is disruptive to family life and quickly burns through goodwill. So best not to overdo it.
PBP is a varied course of average hilliness, never quite flat, but not mountainous. Group riding is often possible, so I'll need aerobic endurance as well as enough leg strength to cope with the hills when very tired. So from June I'm planning to concentrate on rides of 200km or less. I'll try to make some of them challenging. Some will be gratuitously hilly, others will be flat and I'll be aiming to maintain a better average speed. As my spare time is limited, often I'll be simply getting out on my bike for a bit, commuting to work or trying some intervals. What I'm not going to do is make a strict day-by-day plan that I'll never stick to and end up getting annoyed at myself.
taking a weekend out for a really big ride is disruptive to family life and quickly burns through goodwill.