Practice makes perfect, and plenty of food for the bin. I throw away about 90% of the works I start to paint, but I have found the following resources extremely helpful in mastering wet in wet techniques, perspective colour harmony.
These were the books on my bookshelf which I refer to whilst learning to paint:
Finally, I returned from the impressionist aspect of watercolour, to the technical through the many books of Billy Showell.
Detail is the key to her works, and she runs live workshops where you can learn with others and perfect your technique with a master.
When addedd to the basic drawing and observational skills and watercolour techniques mastered through the other books, this is the icing on the cake.