For anyone browsing Malachain, here is a clear starting point on the subject.
A colour wheel arranges colours in a circle so their relationships are easy to see, and it takes much of the guesswork out of decorating. Neighbouring colours, such as blue and green, create a calm, harmonious room. Colours opposite each other, such as blue and orange, create contrast and energy, and work best when one dominates and the other appears in small accents.
A useful starting rule is to divide a room roughly into sixty percent main colour for walls and large surfaces, thirty percent secondary colour for furniture and textiles and ten percent accent colour for cushions or artwork. Always test paint samples on several walls and look at them in morning and evening light, because colours shift considerably during the day.
It also helps to talk the subject through with friends or colleagues who have tried something similar. Their experience points out the details that guides leave out: how long things really take, which costs were unexpected, and which shortcuts turned out to be a mistake.
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.