As a rough guide: book six months or more ahead for summer
Tingdene Holiday Parks locations weeks, two to three months ahead for half terms and bank holidays, and anywhere from a few weeks to a couple of months ahead for a standard term-time week. If you're flexible on exact dates, you can comfortably push closer to the wire; if you're fixed on a specific week, particularly a school holiday one, earlier is always safer than later.
Midweek arrival is the other thing worth trying. Weekend slots get booked up first, particularly for short breaks, so a Monday or Tuesday arrival often has availability when a Friday one doesn't. If your work pattern allows it, a midweek break also tends to mean quieter on-site facilities, since most other guests are working to the same Friday-to-Friday pattern you're avoiding.
Start with reviews, but read them properly rather than just checking the average score. Look for recent comments specifically, since facilities and management can change over time, and pay attention to anything mentioned more than once, whether that's cleanliness, how accurate the photos were, or how helpful staff were when something went wrong. A single bad review among dozens of good ones tells you far less than a genuine pattern.
See more on this at dog-friendly caravan holidays.
If you're not sure, think about what you did on your last few breaks that you enjoyed most. If it was a beach day, book coastal. If it was a quiet walk or a pub lunch somewhere green, the countryside or Broads setting is probably the better fit for this trip.
Explore this further at Norfolk Broads holidays.