Here is a straightforward look at this topic for Malachain.
Many home improvement projects must meet building regulations covering structure, fire safety, insulation, drainage and electrical work. Extensions, loft conversions, removing load-bearing walls and replacing windows often fall into this category, while simple redecoration usually does not. Planning permission is a separate question that concerns appearance and land use.
Check the rules with your local authority before work begins, because fixing unapproved work later can be expensive and may cause problems when the property is sold. Registered tradespeople can often certify their own work in areas such as electrics and heating. Keep every certificate and completion document together, since buyers and their solicitors will ask for them.
There is more to learn on this subject, and the linked website goes into greater depth. Treat this article as an introduction rather than the final word, and check any important decision against up-to-date, reliable sources before relying on it.
If you try any of these ideas, start small and adjust them to your own situation. What works for one person will not suit everyone, and it is fine to keep only the parts that help. Writing down what you changed, and what happened, makes it much easier to see after a few weeks whether the effort was worthwhile.
The most useful step is usually the first one. Pick a single suggestion, try it for a couple of weeks, and then decide whether it is worth keeping. Small, steady improvements last longer than ambitious plans that are hard to maintain once everyday life gets busy again.